diff --git a/README.md b/README.md
index 1144a0cab..11f7b51b9 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@
 - [Discrete Batch-Constrained deep Q-Learning (BCQ-Discrete)](https://arxiv.org/pdf/1910.01708.pdf)
 - [Discrete Conservative Q-Learning (CQL-Discrete)](https://arxiv.org/pdf/2006.04779.pdf)
 - [Discrete Critic Regularized Regression (CRR-Discrete)](https://arxiv.org/pdf/2006.15134.pdf)
+- [Generative Adversarial Imitation Learning (GAIL)](https://arxiv.org/pdf/1606.03476.pdf)
 - [Prioritized Experience Replay (PER)](https://arxiv.org/pdf/1511.05952.pdf)
 - [Generalized Advantage Estimator (GAE)](https://arxiv.org/pdf/1506.02438.pdf)
 - [Posterior Sampling Reinforcement Learning (PSRL)](https://www.ece.uvic.ca/~bctill/papers/learning/Strens_2000.pdf)
diff --git a/docs/api/tianshou.policy.rst b/docs/api/tianshou.policy.rst
index c3063665c..a0d9bed99 100644
--- a/docs/api/tianshou.policy.rst
+++ b/docs/api/tianshou.policy.rst
@@ -134,6 +134,11 @@ Imitation
    :undoc-members:
    :show-inheritance:
 
+.. autoclass:: tianshou.policy.GAILPolicy
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
 Model-based
 -----------
 
diff --git a/docs/index.rst b/docs/index.rst
index 15ac74037..b131ff402 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -32,6 +32,7 @@ Welcome to Tianshou!
 * :class:`~tianshou.policy.DiscreteBCQPolicy` `Discrete Batch-Constrained deep Q-Learning <https://arxiv.org/pdf/1910.01708.pdf>`_
 * :class:`~tianshou.policy.DiscreteCQLPolicy` `Discrete Conservative Q-Learning <https://arxiv.org/pdf/2006.04779.pdf>`_
 * :class:`~tianshou.policy.DiscreteCRRPolicy` `Critic Regularized Regression <https://arxiv.org/pdf/2006.15134.pdf>`_
+* :class:`~tianshou.policy.GAILPolicy` `Generative Adversarial Imitation Learning <https://arxiv.org/pdf/1606.03476.pdf>`_
 * :class:`~tianshou.policy.PSRLPolicy` `Posterior Sampling Reinforcement Learning <https://www.ece.uvic.ca/~bctill/papers/learning/Strens_2000.pdf>`_
 * :class:`~tianshou.policy.ICMPolicy` `Intrinsic Curiosity Module <https://arxiv.org/pdf/1705.05363.pdf>`_
 * :class:`~tianshou.data.PrioritizedReplayBuffer` `Prioritized Experience Replay <https://arxiv.org/pdf/1511.05952.pdf>`_
diff --git a/docs/spelling_wordlist.txt b/docs/spelling_wordlist.txt
index 9f0377b43..86bdb281e 100644
--- a/docs/spelling_wordlist.txt
+++ b/docs/spelling_wordlist.txt
@@ -140,3 +140,6 @@ Strens
 Ornstein
 Uhlenbeck
 mse
+gail
+airl
+ppo
diff --git a/examples/inverse/README.md b/examples/inverse/README.md
new file mode 100644
index 000000000..8e5276bbd
--- /dev/null
+++ b/examples/inverse/README.md
@@ -0,0 +1,27 @@
+# Inverse Reinforcement Learning
+
+In inverse reinforcement learning setting, the agent learns a policy from interaction with an environment without reward and a fixed dataset which is collected with an expert policy.
+
+## Continuous control
+
+Once the dataset is collected, it will not be changed during training. We use [d4rl](https://github.com/rail-berkeley/d4rl) datasets to train agent for continuous control. You can refer to [d4rl](https://github.com/rail-berkeley/d4rl) to see how to use d4rl datasets. 
+
+We provide implementation of GAIL algorithm for continuous control.
+
+### Train
+
+You can parse d4rl datasets into a `ReplayBuffer` , and set it as the parameter `expert_buffer` of `GAILPolicy`.  `irl_gail.py` is an example of inverse RL using the d4rl dataset.
+
+To train an agent with BCQ algorithm:
+
+```bash
+python irl_gail.py --task HalfCheetah-v2 --expert-data-task halfcheetah-expert-v2
+```
+
+## GAIL (single run)
+
+| task                        | best reward | reward curve                          | parameters                                                   |
+| --------------------------- | ----------- | ------------------------------------- | ------------------------------------------------------------ |
+| HalfCheetah-v2     | 5177.07        | ![](results/gail/HalfCheetah-v2_rew.png)         | `python3 irl_gail.py --task "HalfCheetah-v2" --expert-data-task "halfcheetah-expert-v2"` |
+| Hopper-v2          | 1761.44        | ![](results/gail/Hopper-v2_rew.png)     | `python3 irl_gail.py --task "Hopper-v2" --expert-data-task "hopper-expert-v2"` |
+| Walker2d-v2        | 2020.77        | ![](results/gail/Walker2d-v2_rew.png)       | `python3 irl_gail.py --task "Walker2d-v2" --expert-data-task "walker2d-expert-v2"`  |
diff --git a/examples/inverse/irl_gail.py b/examples/inverse/irl_gail.py
new file mode 100644
index 000000000..1e4c0389c
--- /dev/null
+++ b/examples/inverse/irl_gail.py
@@ -0,0 +1,277 @@
+#!/usr/bin/env python3
+
+import argparse
+import datetime
+import os
+import pprint
+
+import d4rl
+import gym
+import numpy as np
+import torch
+from torch import nn
+from torch.distributions import Independent, Normal
+from torch.optim.lr_scheduler import LambdaLR
+from torch.utils.tensorboard import SummaryWriter
+
+from tianshou.data import Batch, Collector, ReplayBuffer, VectorReplayBuffer
+from tianshou.env import SubprocVectorEnv
+from tianshou.policy import GAILPolicy
+from tianshou.trainer import onpolicy_trainer
+from tianshou.utils import TensorboardLogger
+from tianshou.utils.net.common import ActorCritic, Net
+from tianshou.utils.net.continuous import ActorProb, Critic
+
+
+class NoRewardEnv(gym.RewardWrapper):
+    """sets the reward to 0.
+
+    :param gym.Env env: the environment to wrap.
+    """
+
+    def __init__(self, env):
+        super().__init__(env)
+
+    def reward(self, reward):
+        """Set reward to 0."""
+        return np.zeros_like(reward)
+
+
+def get_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--task', type=str, default='HalfCheetah-v2')
+    parser.add_argument('--seed', type=int, default=0)
+    parser.add_argument(
+        '--expert-data-task', type=str, default='halfcheetah-expert-v2'
+    )
+    parser.add_argument('--buffer-size', type=int, default=4096)
+    parser.add_argument('--hidden-sizes', type=int, nargs='*', default=[64, 64])
+    parser.add_argument('--lr', type=float, default=3e-4)
+    parser.add_argument('--disc-lr', type=float, default=2.5e-5)
+    parser.add_argument('--gamma', type=float, default=0.99)
+    parser.add_argument('--epoch', type=int, default=100)
+    parser.add_argument('--step-per-epoch', type=int, default=30000)
+    parser.add_argument('--step-per-collect', type=int, default=2048)
+    parser.add_argument('--repeat-per-collect', type=int, default=10)
+    parser.add_argument('--disc-update-num', type=int, default=2)
+    parser.add_argument('--batch-size', type=int, default=64)
+    parser.add_argument('--training-num', type=int, default=64)
+    parser.add_argument('--test-num', type=int, default=10)
+    # ppo special
+    parser.add_argument('--rew-norm', type=int, default=True)
+    # In theory, `vf-coef` will not make any difference if using Adam optimizer.
+    parser.add_argument('--vf-coef', type=float, default=0.25)
+    parser.add_argument('--ent-coef', type=float, default=0.001)
+    parser.add_argument('--gae-lambda', type=float, default=0.95)
+    parser.add_argument('--bound-action-method', type=str, default="clip")
+    parser.add_argument('--lr-decay', type=int, default=True)
+    parser.add_argument('--max-grad-norm', type=float, default=0.5)
+    parser.add_argument('--eps-clip', type=float, default=0.2)
+    parser.add_argument('--dual-clip', type=float, default=None)
+    parser.add_argument('--value-clip', type=int, default=0)
+    parser.add_argument('--norm-adv', type=int, default=0)
+    parser.add_argument('--recompute-adv', type=int, default=1)
+    parser.add_argument('--logdir', type=str, default='log')
+    parser.add_argument('--render', type=float, default=0.)
+    parser.add_argument(
+        '--device', type=str, default='cuda' if torch.cuda.is_available() else 'cpu'
+    )
+    parser.add_argument('--resume-path', type=str, default=None)
+    parser.add_argument(
+        '--watch',
+        default=False,
+        action='store_true',
+        help='watch the play of pre-trained policy only'
+    )
+    return parser.parse_args()
+
+
+def test_gail(args=get_args()):
+    env = gym.make(args.task)
+    args.state_shape = env.observation_space.shape or env.observation_space.n
+    args.action_shape = env.action_space.shape or env.action_space.n
+    args.max_action = env.action_space.high[0]
+    print("Observations shape:", args.state_shape)
+    print("Actions shape:", args.action_shape)
+    print("Action range:", np.min(env.action_space.low), np.max(env.action_space.high))
+    # train_envs = gym.make(args.task)
+    train_envs = SubprocVectorEnv(
+        [lambda: NoRewardEnv(gym.make(args.task)) for _ in range(args.training_num)],
+        norm_obs=True
+    )
+    # test_envs = gym.make(args.task)
+    test_envs = SubprocVectorEnv(
+        [lambda: gym.make(args.task) for _ in range(args.test_num)],
+        norm_obs=True,
+        obs_rms=train_envs.obs_rms,
+        update_obs_rms=False
+    )
+
+    # seed
+    np.random.seed(args.seed)
+    torch.manual_seed(args.seed)
+    train_envs.seed(args.seed)
+    test_envs.seed(args.seed)
+    # model
+    net_a = Net(
+        args.state_shape,
+        hidden_sizes=args.hidden_sizes,
+        activation=nn.Tanh,
+        device=args.device
+    )
+    actor = ActorProb(
+        net_a,
+        args.action_shape,
+        max_action=args.max_action,
+        unbounded=True,
+        device=args.device
+    ).to(args.device)
+    net_c = Net(
+        args.state_shape,
+        hidden_sizes=args.hidden_sizes,
+        activation=nn.Tanh,
+        device=args.device
+    )
+    critic = Critic(net_c, device=args.device).to(args.device)
+    torch.nn.init.constant_(actor.sigma_param, -0.5)
+    for m in list(actor.modules()) + list(critic.modules()):
+        if isinstance(m, torch.nn.Linear):
+            # orthogonal initialization
+            torch.nn.init.orthogonal_(m.weight, gain=np.sqrt(2))
+            torch.nn.init.zeros_(m.bias)
+    # do last policy layer scaling, this will make initial actions have (close to)
+    # 0 mean and std, and will help boost performances,
+    # see https://arxiv.org/abs/2006.05990, Fig.24 for details
+    for m in actor.mu.modules():
+        if isinstance(m, torch.nn.Linear):
+            torch.nn.init.zeros_(m.bias)
+            m.weight.data.copy_(0.01 * m.weight.data)
+
+    optim = torch.optim.Adam(ActorCritic(actor, critic).parameters(), lr=args.lr)
+    # discriminator
+    net_d = Net(
+        args.state_shape,
+        action_shape=args.action_shape,
+        hidden_sizes=args.hidden_sizes,
+        activation=nn.Tanh,
+        device=args.device,
+        concat=True
+    )
+    disc_net = Critic(net_d, device=args.device).to(args.device)
+    for m in disc_net.modules():
+        if isinstance(m, torch.nn.Linear):
+            # orthogonal initialization
+            torch.nn.init.orthogonal_(m.weight, gain=np.sqrt(2))
+            torch.nn.init.zeros_(m.bias)
+    disc_optim = torch.optim.Adam(disc_net.parameters(), lr=args.disc_lr)
+
+    lr_scheduler = None
+    if args.lr_decay:
+        # decay learning rate to 0 linearly
+        max_update_num = np.ceil(
+            args.step_per_epoch / args.step_per_collect
+        ) * args.epoch
+
+        lr_scheduler = LambdaLR(
+            optim, lr_lambda=lambda epoch: 1 - epoch / max_update_num
+        )
+
+    def dist(*logits):
+        return Independent(Normal(*logits), 1)
+
+    # expert replay buffer
+    dataset = d4rl.qlearning_dataset(gym.make(args.expert_data_task))
+    dataset_size = dataset['rewards'].size
+
+    print("dataset_size", dataset_size)
+    expert_buffer = ReplayBuffer(dataset_size)
+
+    for i in range(dataset_size):
+        expert_buffer.add(
+            Batch(
+                obs=dataset['observations'][i],
+                act=dataset['actions'][i],
+                rew=dataset['rewards'][i],
+                done=dataset['terminals'][i],
+                obs_next=dataset['next_observations'][i],
+            )
+        )
+    print("dataset loaded")
+
+    policy = GAILPolicy(
+        actor,
+        critic,
+        optim,
+        dist,
+        expert_buffer,
+        disc_net,
+        disc_optim,
+        disc_update_num=args.disc_update_num,
+        discount_factor=args.gamma,
+        gae_lambda=args.gae_lambda,
+        max_grad_norm=args.max_grad_norm,
+        vf_coef=args.vf_coef,
+        ent_coef=args.ent_coef,
+        reward_normalization=args.rew_norm,
+        action_scaling=True,
+        action_bound_method=args.bound_action_method,
+        lr_scheduler=lr_scheduler,
+        action_space=env.action_space,
+        eps_clip=args.eps_clip,
+        value_clip=args.value_clip,
+        dual_clip=args.dual_clip,
+        advantage_normalization=args.norm_adv,
+        recompute_advantage=args.recompute_adv
+    )
+
+    # load a previous policy
+    if args.resume_path:
+        policy.load_state_dict(torch.load(args.resume_path, map_location=args.device))
+        print("Loaded agent from: ", args.resume_path)
+
+    # collector
+    if args.training_num > 1:
+        buffer = VectorReplayBuffer(args.buffer_size, len(train_envs))
+    else:
+        buffer = ReplayBuffer(args.buffer_size)
+    train_collector = Collector(policy, train_envs, buffer, exploration_noise=True)
+    test_collector = Collector(policy, test_envs)
+    # log
+    t0 = datetime.datetime.now().strftime("%m%d_%H%M%S")
+    log_file = f'seed_{args.seed}_{t0}-{args.task.replace("-", "_")}_gail'
+    log_path = os.path.join(args.logdir, args.task, 'gail', log_file)
+    writer = SummaryWriter(log_path)
+    writer.add_text("args", str(args))
+    logger = TensorboardLogger(writer, update_interval=100, train_interval=100)
+
+    def save_fn(policy):
+        torch.save(policy.state_dict(), os.path.join(log_path, 'policy.pth'))
+
+    if not args.watch:
+        # trainer
+        result = onpolicy_trainer(
+            policy,
+            train_collector,
+            test_collector,
+            args.epoch,
+            args.step_per_epoch,
+            args.repeat_per_collect,
+            args.test_num,
+            args.batch_size,
+            step_per_collect=args.step_per_collect,
+            save_fn=save_fn,
+            logger=logger,
+            test_in_train=False
+        )
+        pprint.pprint(result)
+
+    # Let's watch its performance!
+    policy.eval()
+    test_envs.seed(args.seed)
+    test_collector.reset()
+    result = test_collector.collect(n_episode=args.test_num, render=args.render)
+    print(f'Final reward: {result["rews"].mean()}, length: {result["lens"].mean()}')
+
+
+if __name__ == '__main__':
+    test_gail()
diff --git a/examples/inverse/results/gail/HalfCheetah-v2_rew.png b/examples/inverse/results/gail/HalfCheetah-v2_rew.png
new file mode 100644
index 000000000..f900a8c1a
Binary files /dev/null and b/examples/inverse/results/gail/HalfCheetah-v2_rew.png differ
diff --git a/examples/inverse/results/gail/Hopper-v2_rew.png b/examples/inverse/results/gail/Hopper-v2_rew.png
new file mode 100644
index 000000000..1cf54253b
Binary files /dev/null and b/examples/inverse/results/gail/Hopper-v2_rew.png differ
diff --git a/examples/inverse/results/gail/Walker2d-v2_rew.png b/examples/inverse/results/gail/Walker2d-v2_rew.png
new file mode 100644
index 000000000..46e711ba7
Binary files /dev/null and b/examples/inverse/results/gail/Walker2d-v2_rew.png differ
diff --git a/test/offline/test_gail.py b/test/offline/test_gail.py
new file mode 100644
index 000000000..f68b7ae74
--- /dev/null
+++ b/test/offline/test_gail.py
@@ -0,0 +1,228 @@
+import argparse
+import os
+import pickle
+import pprint
+
+import gym
+import numpy as np
+import torch
+from torch.distributions import Independent, Normal
+from torch.utils.tensorboard import SummaryWriter
+
+from tianshou.data import Collector, VectorReplayBuffer
+from tianshou.env import DummyVectorEnv
+from tianshou.policy import GAILPolicy
+from tianshou.trainer import onpolicy_trainer
+from tianshou.utils import TensorboardLogger
+from tianshou.utils.net.common import ActorCritic, Net
+from tianshou.utils.net.continuous import ActorProb, Critic
+
+if __name__ == "__main__":
+    from gather_pendulum_data import expert_file_name, gather_data
+else:  # pytest
+    from test.offline.gather_pendulum_data import expert_file_name, gather_data
+
+
+def get_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('--task', type=str, default='Pendulum-v1')
+    parser.add_argument("--reward-threshold", type=float, default=None)
+    parser.add_argument('--seed', type=int, default=1)
+    parser.add_argument('--buffer-size', type=int, default=20000)
+    parser.add_argument('--lr', type=float, default=1e-3)
+    parser.add_argument('--disc-lr', type=float, default=5e-4)
+    parser.add_argument('--gamma', type=float, default=0.95)
+    parser.add_argument('--epoch', type=int, default=5)
+    parser.add_argument('--step-per-epoch', type=int, default=150000)
+    parser.add_argument('--episode-per-collect', type=int, default=16)
+    parser.add_argument('--repeat-per-collect', type=int, default=2)
+    parser.add_argument('--disc-update-num', type=int, default=2)
+    parser.add_argument('--batch-size', type=int, default=128)
+    parser.add_argument('--hidden-sizes', type=int, nargs='*', default=[64, 64])
+    parser.add_argument('--training-num', type=int, default=16)
+    parser.add_argument('--test-num', type=int, default=100)
+    parser.add_argument('--logdir', type=str, default='log')
+    parser.add_argument('--render', type=float, default=0.)
+    parser.add_argument(
+        '--device', type=str, default='cuda' if torch.cuda.is_available() else 'cpu'
+    )
+    # ppo special
+    parser.add_argument('--vf-coef', type=float, default=0.25)
+    parser.add_argument('--ent-coef', type=float, default=0.0)
+    parser.add_argument('--eps-clip', type=float, default=0.2)
+    parser.add_argument('--max-grad-norm', type=float, default=0.5)
+    parser.add_argument('--gae-lambda', type=float, default=0.95)
+    parser.add_argument('--rew-norm', type=int, default=1)
+    parser.add_argument('--dual-clip', type=float, default=None)
+    parser.add_argument('--value-clip', type=int, default=1)
+    parser.add_argument('--norm-adv', type=int, default=1)
+    parser.add_argument('--recompute-adv', type=int, default=0)
+    parser.add_argument('--resume', action="store_true")
+    parser.add_argument("--save-interval", type=int, default=4)
+    parser.add_argument("--load-buffer-name", type=str, default=expert_file_name())
+    args = parser.parse_known_args()[0]
+    return args
+
+
+def test_gail(args=get_args()):
+    if os.path.exists(args.load_buffer_name) and os.path.isfile(args.load_buffer_name):
+        if args.load_buffer_name.endswith(".hdf5"):
+            buffer = VectorReplayBuffer.load_hdf5(args.load_buffer_name)
+        else:
+            buffer = pickle.load(open(args.load_buffer_name, "rb"))
+    else:
+        buffer = gather_data()
+    env = gym.make(args.task)
+    if args.reward_threshold is None:
+        default_reward_threshold = {"Pendulum-v0": -1100, "Pendulum-v1": -1100}
+        args.reward_threshold = default_reward_threshold.get(
+            args.task, env.spec.reward_threshold
+        )
+    args.state_shape = env.observation_space.shape or env.observation_space.n
+    args.action_shape = env.action_space.shape or env.action_space.n
+    args.max_action = env.action_space.high[0]
+    # you can also use tianshou.env.SubprocVectorEnv
+    # train_envs = gym.make(args.task)
+    train_envs = DummyVectorEnv(
+        [lambda: gym.make(args.task) for _ in range(args.training_num)]
+    )
+    # test_envs = gym.make(args.task)
+    test_envs = DummyVectorEnv(
+        [lambda: gym.make(args.task) for _ in range(args.test_num)]
+    )
+    # seed
+    np.random.seed(args.seed)
+    torch.manual_seed(args.seed)
+    train_envs.seed(args.seed)
+    test_envs.seed(args.seed)
+    # model
+    net = Net(args.state_shape, hidden_sizes=args.hidden_sizes, device=args.device)
+    actor = ActorProb(
+        net, args.action_shape, max_action=args.max_action, device=args.device
+    ).to(args.device)
+    critic = Critic(
+        Net(args.state_shape, hidden_sizes=args.hidden_sizes, device=args.device),
+        device=args.device
+    ).to(args.device)
+    actor_critic = ActorCritic(actor, critic)
+    # orthogonal initialization
+    for m in actor_critic.modules():
+        if isinstance(m, torch.nn.Linear):
+            torch.nn.init.orthogonal_(m.weight)
+            torch.nn.init.zeros_(m.bias)
+    optim = torch.optim.Adam(actor_critic.parameters(), lr=args.lr)
+    # discriminator
+    disc_net = Critic(
+        Net(
+            args.state_shape,
+            action_shape=args.action_shape,
+            hidden_sizes=args.hidden_sizes,
+            activation=torch.nn.Tanh,
+            device=args.device,
+            concat=True,
+        ),
+        device=args.device
+    ).to(args.device)
+    for m in disc_net.modules():
+        if isinstance(m, torch.nn.Linear):
+            # orthogonal initialization
+            torch.nn.init.orthogonal_(m.weight, gain=np.sqrt(2))
+            torch.nn.init.zeros_(m.bias)
+    disc_optim = torch.optim.Adam(disc_net.parameters(), lr=args.disc_lr)
+
+    # replace DiagGuassian with Independent(Normal) which is equivalent
+    # pass *logits to be consistent with policy.forward
+    def dist(*logits):
+        return Independent(Normal(*logits), 1)
+
+    policy = GAILPolicy(
+        actor,
+        critic,
+        optim,
+        dist,
+        buffer,
+        disc_net,
+        disc_optim,
+        disc_update_num=args.disc_update_num,
+        discount_factor=args.gamma,
+        max_grad_norm=args.max_grad_norm,
+        eps_clip=args.eps_clip,
+        vf_coef=args.vf_coef,
+        ent_coef=args.ent_coef,
+        reward_normalization=args.rew_norm,
+        advantage_normalization=args.norm_adv,
+        recompute_advantage=args.recompute_adv,
+        dual_clip=args.dual_clip,
+        value_clip=args.value_clip,
+        gae_lambda=args.gae_lambda,
+        action_space=env.action_space,
+    )
+    # collector
+    train_collector = Collector(
+        policy, train_envs, VectorReplayBuffer(args.buffer_size, len(train_envs))
+    )
+    test_collector = Collector(policy, test_envs)
+    # log
+    log_path = os.path.join(args.logdir, args.task, 'gail')
+    writer = SummaryWriter(log_path)
+    logger = TensorboardLogger(writer, save_interval=args.save_interval)
+
+    def save_fn(policy):
+        torch.save(policy.state_dict(), os.path.join(log_path, 'policy.pth'))
+
+    def stop_fn(mean_rewards):
+        return mean_rewards >= args.reward_threshold
+
+    def save_checkpoint_fn(epoch, env_step, gradient_step):
+        # see also: https://pytorch.org/tutorials/beginner/saving_loading_models.html
+        torch.save(
+            {
+                'model': policy.state_dict(),
+                'optim': optim.state_dict(),
+            }, os.path.join(log_path, 'checkpoint.pth')
+        )
+
+    if args.resume:
+        # load from existing checkpoint
+        print(f"Loading agent under {log_path}")
+        ckpt_path = os.path.join(log_path, 'checkpoint.pth')
+        if os.path.exists(ckpt_path):
+            checkpoint = torch.load(ckpt_path, map_location=args.device)
+            policy.load_state_dict(checkpoint['model'])
+            optim.load_state_dict(checkpoint['optim'])
+            print("Successfully restore policy and optim.")
+        else:
+            print("Fail to restore policy and optim.")
+
+    # trainer
+    result = onpolicy_trainer(
+        policy,
+        train_collector,
+        test_collector,
+        args.epoch,
+        args.step_per_epoch,
+        args.repeat_per_collect,
+        args.test_num,
+        args.batch_size,
+        episode_per_collect=args.episode_per_collect,
+        stop_fn=stop_fn,
+        save_fn=save_fn,
+        logger=logger,
+        resume_from_log=args.resume,
+        save_checkpoint_fn=save_checkpoint_fn,
+    )
+    assert stop_fn(result['best_reward'])
+
+    if __name__ == '__main__':
+        pprint.pprint(result)
+        # Let's watch its performance!
+        env = gym.make(args.task)
+        policy.eval()
+        collector = Collector(policy, env)
+        result = collector.collect(n_episode=1, render=args.render)
+        rews, lens = result["rews"], result["lens"]
+        print(f"Final reward: {rews.mean()}, length: {lens.mean()}")
+
+
+if __name__ == '__main__':
+    test_gail()
diff --git a/tianshou/policy/__init__.py b/tianshou/policy/__init__.py
index ced11aff5..dae9da638 100644
--- a/tianshou/policy/__init__.py
+++ b/tianshou/policy/__init__.py
@@ -24,6 +24,7 @@
 from tianshou.policy.imitation.discrete_bcq import DiscreteBCQPolicy
 from tianshou.policy.imitation.discrete_cql import DiscreteCQLPolicy
 from tianshou.policy.imitation.discrete_crr import DiscreteCRRPolicy
+from tianshou.policy.imitation.gail import GAILPolicy
 from tianshou.policy.modelbased.psrl import PSRLPolicy
 from tianshou.policy.modelbased.icm import ICMPolicy
 from tianshou.policy.multiagent.mapolicy import MultiAgentPolicyManager
@@ -52,6 +53,7 @@
     "DiscreteBCQPolicy",
     "DiscreteCQLPolicy",
     "DiscreteCRRPolicy",
+    "GAILPolicy",
     "PSRLPolicy",
     "ICMPolicy",
     "MultiAgentPolicyManager",
diff --git a/tianshou/policy/imitation/gail.py b/tianshou/policy/imitation/gail.py
new file mode 100644
index 000000000..d4779326b
--- /dev/null
+++ b/tianshou/policy/imitation/gail.py
@@ -0,0 +1,139 @@
+from typing import Any, Dict, List, Optional, Type
+
+import numpy as np
+import torch
+import torch.nn.functional as F
+
+from tianshou.data import Batch, ReplayBuffer, to_numpy, to_torch
+from tianshou.policy import PPOPolicy
+
+
+class GAILPolicy(PPOPolicy):
+    r"""Implementation of Generative Adversarial Imitation Learning. arXiv:1606.03476.
+
+    :param torch.nn.Module actor: the actor network following the rules in
+        :class:`~tianshou.policy.BasePolicy`. (s -> logits)
+    :param torch.nn.Module critic: the critic network. (s -> V(s))
+    :param torch.optim.Optimizer optim: the optimizer for actor and critic network.
+    :param dist_fn: distribution class for computing the action.
+    :type dist_fn: Type[torch.distributions.Distribution]
+    :param ReplayBuffer expert_buffer: the replay buffer contains expert experience.
+    :param torch.nn.Module disc_net: the discriminator network with input dim equals
+        state dim plus action dim and output dim equals 1.
+    :param torch.optim.Optimizer disc_optim: the optimizer for the discriminator
+        network.
+    :param int disc_update_num: the number of discriminator grad steps per model grad
+        step. Default to 4.
+    :param float discount_factor: in [0, 1]. Default to 0.99.
+    :param float eps_clip: :math:`\epsilon` in :math:`L_{CLIP}` in the original
+        paper. Default to 0.2.
+    :param float dual_clip: a parameter c mentioned in arXiv:1912.09729 Equ. 5,
+        where c > 1 is a constant indicating the lower bound.
+        Default to 5.0 (set None if you do not want to use it).
+    :param bool value_clip: a parameter mentioned in arXiv:1811.02553 Sec. 4.1.
+        Default to True.
+    :param bool advantage_normalization: whether to do per mini-batch advantage
+        normalization. Default to True.
+    :param bool recompute_advantage: whether to recompute advantage every update
+        repeat according to https://arxiv.org/pdf/2006.05990.pdf Sec. 3.5.
+        Default to False.
+    :param float vf_coef: weight for value loss. Default to 0.5.
+    :param float ent_coef: weight for entropy loss. Default to 0.01.
+    :param float max_grad_norm: clipping gradients in back propagation. Default to
+        None.
+    :param float gae_lambda: in [0, 1], param for Generalized Advantage Estimation.
+        Default to 0.95.
+    :param bool reward_normalization: normalize estimated values to have std close
+        to 1, also normalize the advantage to Normal(0, 1). Default to False.
+    :param int max_batchsize: the maximum size of the batch when computing GAE,
+        depends on the size of available memory and the memory cost of the model;
+        should be as large as possible within the memory constraint. Default to 256.
+    :param bool action_scaling: whether to map actions from range [-1, 1] to range
+        [action_spaces.low, action_spaces.high]. Default to True.
+    :param str action_bound_method: method to bound action to range [-1, 1], can be
+        either "clip" (for simply clipping the action), "tanh" (for applying tanh
+        squashing) for now, or empty string for no bounding. Default to "clip".
+    :param Optional[gym.Space] action_space: env's action space, mandatory if you want
+        to use option "action_scaling" or "action_bound_method". Default to None.
+    :param lr_scheduler: a learning rate scheduler that adjusts the learning rate in
+        optimizer in each policy.update(). Default to None (no lr_scheduler).
+    :param bool deterministic_eval: whether to use deterministic action instead of
+        stochastic action sampled by the policy. Default to False.
+
+    .. seealso::
+
+        Please refer to :class:`~tianshou.policy.PPOPolicy` for more detailed
+        explanation.
+    """
+
+    def __init__(
+        self,
+        actor: torch.nn.Module,
+        critic: torch.nn.Module,
+        optim: torch.optim.Optimizer,
+        dist_fn: Type[torch.distributions.Distribution],
+        expert_buffer: ReplayBuffer,
+        disc_net: torch.nn.Module,
+        disc_optim: torch.optim.Optimizer,
+        disc_update_num: int = 4,
+        eps_clip: float = 0.2,
+        dual_clip: Optional[float] = None,
+        value_clip: bool = False,
+        advantage_normalization: bool = True,
+        recompute_advantage: bool = False,
+        **kwargs: Any,
+    ) -> None:
+        super().__init__(
+            actor, critic, optim, dist_fn, eps_clip, dual_clip, value_clip,
+            advantage_normalization, recompute_advantage, **kwargs
+        )
+        self.disc_net = disc_net
+        self.disc_optim = disc_optim
+        self.disc_update_num = disc_update_num
+        self.expert_buffer = expert_buffer
+        self.action_dim = actor.output_dim
+
+    def process_fn(
+        self, batch: Batch, buffer: ReplayBuffer, indices: np.ndarray
+    ) -> Batch:
+        """Pre-process the data from the provided replay buffer.
+
+        Used in :meth:`update`. Check out :ref:`process_fn` for more information.
+        """
+        # update reward
+        with torch.no_grad():
+            batch.rew = to_numpy(-F.logsigmoid(-self.disc(batch)).flatten())
+        return super().process_fn(batch, buffer, indices)
+
+    def disc(self, batch: Batch) -> torch.Tensor:
+        obs = to_torch(batch.obs, device=self.disc_net.device)  # type: ignore
+        act = to_torch(batch.act, device=self.disc_net.device)  # type: ignore
+        return self.disc_net(torch.cat([obs, act], dim=1))  # type: ignore
+
+    def learn(  # type: ignore
+        self, batch: Batch, batch_size: int, repeat: int, **kwargs: Any
+    ) -> Dict[str, List[float]]:
+        # update discriminator
+        losses = []
+        acc_pis = []
+        acc_exps = []
+        bsz = len(batch) // self.disc_update_num
+        for b in batch.split(bsz, merge_last=True):
+            logits_pi = self.disc(b)
+            exp_b = self.expert_buffer.sample(bsz)[0]
+            logits_exp = self.disc(exp_b)
+            loss_pi = -F.logsigmoid(-logits_pi).mean()
+            loss_exp = -F.logsigmoid(logits_exp).mean()
+            loss_disc = loss_pi + loss_exp
+            self.disc_optim.zero_grad()
+            loss_disc.backward()
+            self.disc_optim.step()
+            losses.append(loss_disc.item())
+            acc_pis.append((logits_pi < 0).float().mean().item())
+            acc_exps.append((logits_exp > 0).float().mean().item())
+        # update policy
+        res = super().learn(batch, batch_size, repeat, **kwargs)
+        res["loss/disc"] = losses
+        res["stats/acc_pi"] = acc_pis
+        res["stats/acc_exp"] = acc_exps
+        return res