diff --git a/brax/experimental/barkour/tutorial.ipynb b/brax/experimental/barkour/tutorial.ipynb
index 34061b5f..6b0d5df1 100644
--- a/brax/experimental/barkour/tutorial.ipynb
+++ b/brax/experimental/barkour/tutorial.ipynb
@@ -814,7 +814,7 @@
       },
       "outputs": [],
       "source": [
-        "HTML(html.render(eval_env.sys.replace(dt=eval_env.dt), rollout))"
+        "HTML(html.render(eval_env.sys.tree_replace({'opt.timestep': eval_env.dt}), rollout))"
       ]
     }
   ],
diff --git a/brax/training/agents/ppo/train.py b/brax/training/agents/ppo/train.py
index 93fd050f..90ce5cd4 100644
--- a/brax/training/agents/ppo/train.py
+++ b/brax/training/agents/ppo/train.py
@@ -35,11 +35,13 @@
 from brax.training.types import Params
 from brax.training.types import PRNGKey
 from brax.v1 import envs as envs_v1
+from etils import epath
 import flax
 import jax
 import jax.numpy as jnp
 import numpy as np
 import optax
+from orbax import checkpoint as ocp
 
 
 InferenceParams = Tuple[running_statistics.NestedMeanStd, Params]
@@ -103,6 +105,7 @@ def train(
     randomization_fn: Optional[
         Callable[[base.System, jnp.ndarray], Tuple[base.System, base.System]]
     ] = None,
+    restore_checkpoint_path: Optional[str] = None,
 ):
   """PPO training.
 
@@ -122,8 +125,8 @@ def train(
     num_eval_envs: the number of envs to use for evluation. Each env will run 1
       episode, and all envs run in parallel during eval.
     learning_rate: learning rate for ppo loss
-    entropy_cost: entropy reward for ppo loss, higher values increase entropy
-      of the policy
+    entropy_cost: entropy reward for ppo loss, higher values increase entropy of
+      the policy
     discounting: discounting rate
     seed: random seed
     unroll_length: the number of timesteps to unroll in each environment. The
@@ -151,6 +154,7 @@ def train(
       saving policy checkpoints
     randomization_fn: a user-defined callback function that generates randomized
       environments
+    restore_checkpoint_path: the path used to restore previous model params
 
   Returns:
     Tuple of (make_policy function, network params, metrics)
@@ -365,15 +369,40 @@ def training_epoch_with_timing(
     }
     return training_state, env_state, metrics  # pytype: disable=bad-return-type  # py311-upgrade
 
+  # Initialize model params and training state.
   init_params = ppo_losses.PPONetworkParams(
       policy=ppo_network.policy_network.init(key_policy),
-      value=ppo_network.value_network.init(key_value))
+      value=ppo_network.value_network.init(key_value),
+  )
+
   training_state = TrainingState(  # pytype: disable=wrong-arg-types  # jax-ndarray
       optimizer_state=optimizer.init(init_params),  # pytype: disable=wrong-arg-types  # numpy-scalars
       params=init_params,
       normalizer_params=running_statistics.init_state(
           specs.Array(env_state.obs.shape[-1:], jnp.dtype('float32'))),
       env_steps=0)
+
+  if num_timesteps == 0:
+    return (
+        make_policy,
+        (training_state.normalizer_params, training_state.params),
+        {},
+    )
+
+  if (
+      restore_checkpoint_path is not None
+      and epath.Path(restore_checkpoint_path).exists()
+  ):
+    logging.info('restoring from checkpoint %s', restore_checkpoint_path)
+    orbax_checkpointer = ocp.PyTreeCheckpointer()
+    target = training_state.normalizer_params, init_params
+    (normalizer_params, init_params) = orbax_checkpointer.restore(
+        restore_checkpoint_path, item=target
+    )
+    training_state = training_state.replace(
+        normalizer_params=normalizer_params, params=init_params
+    )
+
   training_state = jax.device_put_replicated(
       training_state,
       jax.local_devices()[:local_devices_to_use])
@@ -439,7 +468,8 @@ def training_epoch_with_timing(
       logging.info(metrics)
       progress_fn(current_step, metrics)
       params = _unpmap(
-          (training_state.normalizer_params, training_state.params.policy))
+          (training_state.normalizer_params, training_state.params)
+      )
       policy_params_fn(current_step, make_policy, params)
 
   total_steps = current_step
diff --git a/brax/training/learner.py b/brax/training/learner.py
index d3fce1be..9dd3c3c5 100644
--- a/brax/training/learner.py
+++ b/brax/training/learner.py
@@ -272,7 +272,7 @@ def do_rollout(rng):
     for i in range(FLAGS.num_videos):
       html_path = f'{FLAGS.logdir}/saved_videos/trajectory_{i:04d}.html'
       if isinstance(env, envs.Env):
-        html.save(html_path, env.sys.replace(dt=env.dt), trajectories[i])
+        html.save(html_path, env.sys.tree_replace({'opt.timestep': env.dt}), trajectories[i])
       else:
         html_v1.save_html(html_path, env.sys, trajectories[i], make_dir=True)
   elif FLAGS.num_videos > 0:
diff --git a/docs/release-notes/next-release.md b/docs/release-notes/next-release.md
index ca4ecb57..d1d52cac 100644
--- a/docs/release-notes/next-release.md
+++ b/docs/release-notes/next-release.md
@@ -1 +1,4 @@
 # Brax Release Notes
+
+* Modify `policy_params_fn` in the PPO implementation to take in the full model params. This can be used for checkpointing models.
+* Add `restore_checkpoint_path` in PPO implementation.
diff --git a/notebooks/training.ipynb b/notebooks/training.ipynb
index bde1e0c9..b71e640d 100644
--- a/notebooks/training.ipynb
+++ b/notebooks/training.ipynb
@@ -424,7 +424,7 @@
         "  act, _ = jit_inference_fn(state.obs, act_rng)\n",
         "  state = jit_env_step(state, act)\n",
         "\n",
-        "HTML(html.render(env.sys.replace(dt=env.dt), rollout))"
+        "HTML(html.render(env.sys.tree_replace({'opt.timestep': env.dt}), rollout))"
       ]
     },
     {
@@ -437,7 +437,7 @@
       ]
     }
   ],
- "metadata": {
+  "metadata": {
     "colab": {
       "provenance": [],
       "toc_visible": true
diff --git a/setup.py b/setup.py
index 97880626..270daf17 100644
--- a/setup.py
+++ b/setup.py
@@ -56,6 +56,7 @@
         "mujoco-mjx",
         "numpy",
         "optax",
+        "orbax-checkpoint",
         # TODO: remove pytinyrenderer after dropping legacy v1 code
         "Pillow",
         "pytinyrenderer",