diff --git a/config/main.yaml b/config/main.yaml
index 22c106d3..6aa52c09 100644
--- a/config/main.yaml
+++ b/config/main.yaml
@@ -2,7 +2,7 @@ defaults:
   - _self_
   - env: grid
   - gflownet: trajectorybalance
-  - policy: mlp_${gflownet}
+  - policy: mlp
   - proxy: uniform
   - logger: wandb
   - user: default
diff --git a/config/policy/base.yaml b/config/policy/base.yaml
new file mode 100644
index 00000000..c2b746f1
--- /dev/null
+++ b/config/policy/base.yaml
@@ -0,0 +1,5 @@
+_target_: gflownet.policy.base.Policy
+
+base: null
+shared_weights: False
+checkpoint: null
diff --git a/config/policy/cnn.yaml b/config/policy/cnn.yaml
index 98818bd8..6874e484 100644
--- a/config/policy/cnn.yaml
+++ b/config/policy/cnn.yaml
@@ -1,16 +1,11 @@
-_target_: gflownet.policy.cnn.CNNPolicy
-
-shared: null
+defaults:
+  - base
 
-forward:
-  n_layers: 2
-  channels: [16, 32]
-  kernel_sizes: [[3, 3], [2, 2]]  # Each tuple represents (height, width)
-  strides: [[1, 1], [1, 1]]  # Each tuple represents (vertical_stride, horizontal_stride)
-  checkpoint: null
-  reload_ckpt: False
+_target_: gflownet.policy.cnn.CNNPolicy
 
-backward:
-  shared_weights: True
-  checkpoint: null
-  reload_ckpt: False
+n_layers: 2
+channels: [16, 32]
+# Kernels: Each tuple represents (height, width)
+kernels: [[3, 3], [2, 2]]
+# Strides: Each tuple represents (vertical_stride, horizontal_stride)
+strides: [[1, 1], [1, 1]]
diff --git a/config/policy/mlp.yaml b/config/policy/mlp.yaml
index b9e2f9a6..b9ecc99f 100644
--- a/config/policy/mlp.yaml
+++ b/config/policy/mlp.yaml
@@ -1,11 +1,8 @@
-_target_: gflownet.policy.mlp.MLPPolicy
-
-shared: null
+defaults:
+  - base
 
-forward:
-  n_hid: 128
-  n_layers: 2
-  checkpoint: null
-  reload_ckpt: False
+_target_: gflownet.policy.mlp.MLPPolicy
 
-backward: null
+n_hid: 128
+n_layers: 2
+tail: []
diff --git a/gflownet/policy/base.py b/gflownet/policy/base.py
index 5d26e0c1..a6ea4971 100644
--- a/gflownet/policy/base.py
+++ b/gflownet/policy/base.py
@@ -15,19 +15,18 @@
 class Policy:
     def __init__(
         self,
-        config: Union[dict, DictConfig],
         env: GFlowNetEnv,
         device: Union[str, torch.device],
         float_precision: [int, torch.dtype],
         base=None,
+        shared_weights: bool = False,
+        checkpoint: str = None,
     ):
         """
         Base Policy class for a :class:`GFlowNetAgent`.
 
         Parameters
         ----------
-        config : dict or DictConfig
-            The configuration dictionary to set up the policy model.
         env : GFlowNetEnv
             The environment used to train the :class:`GFlowNetAgent`, used to extract
             needed properties.
@@ -37,8 +36,12 @@ def __init__(
             The floating point precision to be passed to torch tensors.
         base: Policy (optional)
             A base policy to be used as backbone for the backward policy.
+        shared_weights: bool (optional)
+            Whether the weights of the backward policy are shared with the (base)
+            forward policy model. Defaults to False.
+        checkpoint: str (optional)
+            The path the a checkpoint file to be reloaded as the policy model.
         """
-        config = self._get_config(config)
         # Device and float precision
         self.device = set_device(device)
         self.float = set_float_precision(float_precision)
@@ -49,36 +52,17 @@ def __init__(
         self.output_dim = len(self.fixed_output)
         # Optional base model
         self.base = base
-        # Policy type, defaults to uniform
-        self.type = config.get("type", "uniform")
+        # Shared weights, defaults to False
+        self.shared_weights = shared_weights
         # Checkpoint, defaults to None
-        self.checkpoint = config.get("checkpoint", None)
+        self.checkpoint = checkpoint
         # Instantiate the model
         self.model, self.is_model = self.make_model()
 
-    @staticmethod
-    def _get_config(config: Union[dict, DictConfig]) -> Union[dict, DictConfig]:
-        """
-        Returns a configuration dictionary, even if the input is None.
-
-        Parameters
-        ----------
-        config : dict or DictConfig
-            The configuration dictionary to set up the policy model. It may be None, in
-            which an empty config is created and the defaults will be used.
-
-        Returns
-        -------
-        config : dict or DictConfig
-            The configuration dictionary to set up the policy model.
-        """
-        if config is None:
-            config = OmegaConf.create()
-        return config
-
+    @abstractmethod
     def make_model(self) -> Tuple[Union[torch.Tensor, torch.nn.Module], bool]:
         """
-        Instantiates the model of the policy.
+        Instantiates the model or fixed tensor of the policy.
 
         Returns
         -------
@@ -88,51 +72,15 @@ def make_model(self) -> Tuple[Union[torch.Tensor, torch.nn.Module], bool]:
             True if the policy is a model (for example, a neural network) and False if
             it is a fixed tensor (for example to make a uniform distribution).
         """
-        if self.type == "fixed":
-            return self.fixed_distribution, False
-        elif self.type == "uniform":
-            return self.uniform_distribution, False
-        else:
-            raise "Policy model type not defined"
-
-    def __call__(self, states):
-        return self.model(states)
-
-    def fixed_distribution(self, states):
-        """
-        Returns the fixed distribution specified by the environment.
-
-        Parameters
-        ----------
-        states : tensor
-            The states for which the fixed distribution is to be returned
-        """
-        return torch.tile(self.fixed_output, (len(states), 1)).to(
-            dtype=self.float, device=self.device
-        )
-
-    def random_distribution(self, states):
-        """
-        Returns the random distribution specified by the environment.
-
-        Parameters
-        ----------
-        states : tensor
-            The states for which the random distribution is to be returned
-        """
-        return torch.tile(self.random_output, (len(states), 1)).to(
-            dtype=self.float, device=self.device
-        )
+        pass
 
-    def uniform_distribution(self, states):
+    def __call__(self, states: torch.Tensor):
         """
-        Return action logits (log probabilities) from a uniform distribution
+        Returns the outputs of the policy model on a batch of states.
 
         Parameters
         ----------
-        states : tensor
-            The states for which the uniform distribution is to be returned
+        states : torch.Tensor
+            A batch of states in policy format.
         """
-        return torch.ones(
-            (len(states), self.output_dim), dtype=self.float, device=self.device
-        )
+        return self.model(states)
diff --git a/gflownet/policy/cnn.py b/gflownet/policy/cnn.py
index 52693fc3..d9ce142e 100644
--- a/gflownet/policy/cnn.py
+++ b/gflownet/policy/cnn.py
@@ -6,17 +6,47 @@
 
 
 class CNNPolicy(Policy):
-    def __init__(self, **kwargs):
-        config = self._get_config(kwargs["config"])
-        # Shared weights, defaults to False
-        self.shared_weights = config.get("shared_weights", False)
-        # Reload checkpoint, defaults to False
-        self.reload_ckpt = config.get("reload_ckpt", False)
+    def __init__(
+        self,
+        n_layers: int = 2,
+        channels: Union[int, List] = [16, 32],
+        kernels: Union[int, List] =  [[3, 3], [2, 2]],
+        strides: Union[int, List] = [[1, 1], [1, 1]],
+        **kwargs,
+    ):
+        """
+        CNN Policy class for a :class:`GFlowNetAgent`.
+
+        Parameters
+        ----------
+        n_layers : int
+            The number of layers in the CNN architecture.
+        channels : int or list
+            The number of channels in the convolutional layers or a list of number of
+            channels for each layer.
+        kernels : int or list
+            The kernel size of the convolutions or a list of kernel sizes for each
+            layer.
+        strides : int or list
+            The stride of the convolutions or a list of strides for each layer.
+        """
         # CNN features: number of layers, number of channels, kernel sizes, strides
-        self.n_layers = config.get("n_layers", 3)
-        self.channels = config.get("channels", [16] * self.n_layers)
-        self.kernel_sizes = config.get("kernel_sizes", [(3, 3)] * self.n_layers)
-        self.strides = config.get("strides", [(1, 1)] * self.n_layers)
+        self.n_layers = n_layers
+        if isinstance(channels, int):
+            self.channels = [channels] * self.n_layers
+        else:
+            # TODO: check if valid
+            self.channels = channels
+        if isinstance(kernels, int):
+            self.kernels = [(kernels, kernels)] * self.n_layers
+        else:
+            # TODO: check if valid
+            self.kernels = kernels
+        if isinstance(strides, int):
+            self.strides = [(stride, stride)] * self.n_layers
+        else:
+            # TODO: check if valid
+            self.strides = strides
         # Environment
         # TODO: rethink whether storing the whole environment is needed
         self.env = env
@@ -46,10 +76,10 @@ def make_model(self):
         current_channels = 1
         conv_module = nn.Sequential()
 
-        if len(self.kernel_sizes) != self.n_layers:
+        if len(self.kernels) != self.n_layers:
             raise ValueError(
-                f"Inconsistent dimensions kernel_sizes != n_layers, "
-                "{len(self.kernel_sizes)} != {self.n_layers}"
+                f"Inconsistent dimensions kernels != n_layers, "
+                "{len(self.kernels)} != {self.n_layers}"
             )
 
         for i in range(self.n_layers):
@@ -58,7 +88,7 @@ def make_model(self):
                 nn.Conv2d(
                     in_channels=current_channels,
                     out_channels=self.channels[i],
-                    kernel_size=tuple(self.kernel_sizes[i]),
+                    kernel_size=tuple(self.kernels[i]),
                     stride=tuple(self.strides[i]),
                     padding=0,
                     padding_mode="zeros",  # Constant zero padding
diff --git a/gflownet/policy/fixed.py b/gflownet/policy/fixed.py
new file mode 100644
index 00000000..015aff5b
--- /dev/null
+++ b/gflownet/policy/fixed.py
@@ -0,0 +1,25 @@
+from gflownet.policy.base import Policy
+
+
+class FixedPolicy(Policy):
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+
+    def make_model(self):
+        """
+        Instantiates the policy model as a fixed tensor with the values of
+        `self.fixed_output` defined by the environment.
+
+        Returns
+        -------
+        model : torch.tensor
+            The tensor `self.fixed_output` defined by the environment.
+        is_model : bool
+            False, because the policy is not a model.
+        """
+        return (
+            torch.tile(self.fixed_output, (len(states), 1)).to(
+                dtype=self.float, device=self.device
+            ),
+            False,
+        )
diff --git a/gflownet/policy/mlp.py b/gflownet/policy/mlp.py
index 8f4fbc80..e94215c8 100644
--- a/gflownet/policy/mlp.py
+++ b/gflownet/policy/mlp.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from omegaconf import OmegaConf
 from torch import nn
 
@@ -5,16 +7,23 @@
 
 
 class MLPPolicy(Policy):
-    def __init__(self, **kwargs):
-        config = self._get_config(kwargs["config"])
-        # Shared weights, defaults to False
-        self.shared_weights = config.get("shared_weights", False)
-        # Reload checkpoint, defaults to False
-        self.reload_ckpt = config.get("reload_ckpt", False)
+    def __init__(self, n_layers: int = 2, n_hid: int = 128, tail: List = [], **kwargs):
+        """
+        MLP Policy class for a :class:`GFlowNetAgent`.
+
+        Parameters
+        ----------
+        n_layers : int
+            The number of layers in the MLP architecture.
+        n_hid : int
+            The number of hidden units per layer.
+        tail : list
+            A list of layers to conform the top (tail) of the MLP architecture.
+        """
         # MLP features: number of layers, number of hidden units, tail, etc.
-        self.n_layers = config.get("n_layers", 2)
-        self.n_hid = config.get("n_hid", 128)
-        self.tail = config.get("tail", [])
+        self.n_layers = n_layers
+        self.n_hid = n_hid
+        self.tail = tail
         # Base init
         super().__init__(**kwargs)
 
@@ -71,6 +80,3 @@ def make_model(self, activation: nn.Module = nn.LeakyReLU()):
             raise ValueError(
                 "Base Model must be provided when shared_weights is set to True"
             )
-
-    def __call__(self, states):
-        return self.model(states)
diff --git a/gflownet/policy/random.py b/gflownet/policy/random.py
new file mode 100644
index 00000000..e87dcbc0
--- /dev/null
+++ b/gflownet/policy/random.py
@@ -0,0 +1,25 @@
+from gflownet.policy.base import Policy
+
+
+class RandomPolicy(Policy):
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+
+    def make_model(self):
+        """
+        Instantiates the policy model as a fixed tensor with the values of
+        `self.random_output` defined by the environment.
+
+        Returns
+        -------
+        model : torch.tensor
+            The tensor `self.random_output` defined by the environment.
+        is_model : bool
+            False, because the policy is not a model.
+        """
+        return (
+            torch.tile(self.random_output, (len(states), 1)).to(
+                dtype=self.float, device=self.device
+            ),
+            False,
+        )
diff --git a/gflownet/policy/uniform.py b/gflownet/policy/uniform.py
new file mode 100644
index 00000000..f901905b
--- /dev/null
+++ b/gflownet/policy/uniform.py
@@ -0,0 +1,25 @@
+from gflownet.policy.base import Policy
+
+
+class UniformPolicy(Policy):
+    def __init__(self, **kwargs):
+        super().__init__(**kwargs)
+
+    def make_model(self):
+        """
+        Instantiates the policy model as a fixed tensor of ones, to define a uniform
+        distribution over the action space.
+
+        Returns
+        -------
+        model : torch.tensor
+            A tensor of `self.output_dim` ones.
+        is_model : bool
+            False, because the policy is not a model.
+        """
+        return (
+            torch.ones(
+                (len(states), self.output_dim), dtype=self.float, device=self.device
+            ),
+            False,
+        )