diff --git a/pina/condition/__init__.py b/pina/condition/__init__.py
index 36f4011..ce339be 100644
--- a/pina/condition/__init__.py
+++ b/pina/condition/__init__.py
@@ -1,5 +1,5 @@
 """
-Module for conditions.
+Module for importing Conditions objects.
 """
 
 __all__ = [
diff --git a/pina/condition/condition.py b/pina/condition/condition.py
index 53744b4..ccb5d14 100644
--- a/pina/condition/condition.py
+++ b/pina/condition/condition.py
@@ -1,4 +1,6 @@
-"""Condition module."""
+"""
+Condition module.
+"""
 
 import warnings
 from .data_condition import DataCondition
@@ -13,12 +15,11 @@ warnings.filterwarnings("always", category=DeprecationWarning)
 
 
 def warning_function(new, old):
-    """Handle the deprecation warning.
+    """
+    Handle the deprecation warning.
 
-    :param new: Object to use instead of the old one.
-    :type new: str
-    :param old: Object to deprecate.
-    :type old: str
+    :param str new: Object to use instead of the old one.
+    :param str old: Object to deprecate.
     """
     warnings.warn(
         f"'{old}' is deprecated and will be removed "
@@ -72,7 +73,6 @@ class Condition:
     ...     input=data,
     ...     conditional_variables=conditional_variables
     ... )
-
     """
 
     __slots__ = list(
@@ -85,7 +85,19 @@ class Condition:
     )
 
     def __new__(cls, *args, **kwargs):
+        """
+        Create a new condition object based on the keyword arguments passed.
+        - ``input`` and ``target``: :class:`InputTargetCondition`
+        - ``domain`` and ``equation``: :class:`DomainEquationCondition`
+        - ``input`` and ``equation``: :class:`InputEquationCondition`
+        - ``input``: :class:`DataCondition`
+        - ``input`` and ``conditional_variables``: :class:`DataCondition`
 
+        :raises ValueError: No valid condition has been found.
+        :return: A new condition instance belonging to the proper class.
+        :rtype: ConditionInputTarget | ConditionInputEquation |
+            ConditionDomainEquation | ConditionData
+        """
         if len(args) != 0:
             raise ValueError(
                 "Condition takes only the following keyword "
diff --git a/pina/condition/condition_interface.py b/pina/condition/condition_interface.py
index 4d748c3..382eb75 100644
--- a/pina/condition/condition_interface.py
+++ b/pina/condition/condition_interface.py
@@ -21,17 +21,36 @@ class ConditionInterface(metaclass=ABCMeta):
         """
         Return the problem to which the condition is associated.
 
-        :return: Problem to which the condition is associated
+        :return: Problem to which the condition is associated.
         :rtype: pina.problem.AbstractProblem
         """
+
         return self._problem
 
     @problem.setter
     def problem(self, value):
+        """
+        Set the problem to which the condition is associated.
+
+        :param value: Problem to which the condition is associated.
+        :type value: pina.problem.AbstractProblem
+        """
+
         self._problem = value
 
     @staticmethod
     def _check_graph_list_consistency(data_list):
+        """
+        Check if the list of Data/Graph objects is consistent.
+
+        :param data_list: list of Data/Graph objects.
+        :type data_list: list(Data) | list(Graph)
+
+        :raises ValueError: Input data must be either Data or Graph objects.
+        :raises ValueError: All elements in the list must have the same keys.
+        :raises ValueError: Type mismatch in data tensors.
+        :raises ValueError: Label mismatch in LabelTensors.
+        """
 
         # If the data is a Graph or Data object, return (do not need to check
         # anything)
diff --git a/pina/condition/data_condition.py b/pina/condition/data_condition.py
index 1560157..b43bfd1 100644
--- a/pina/condition/data_condition.py
+++ b/pina/condition/data_condition.py
@@ -23,17 +23,20 @@ class DataCondition(ConditionInterface):
 
     def __new__(cls, input, conditional_variables=None):
         """
-        Instanciate the correct subclass of DataCondition by checking the type
-        of the input data (input and conditional_variables).
+        Instantiate the appropriate subclass of DataCondition based on the
+        types of input data.
+
+        :param input: Input data for the condition.
+        :type input: torch.Tensor | LabelTensor | Graph | Data
+        :param conditional_variables: Conditional variables for the condition.
+        :type conditional_variables: torch.Tensor | LabelTensor
+        :return: Subclass of DataCondition.
+        :rtype: TensorDataCondition | GraphDataCondition
+
+        :raises ValueError: If input is not of type :class:`torch.Tensor`,
+            :class:`LabelTensor`, :class:`Graph`, or :class:`Data`.
+
 
-        :param input: torch.Tensor or Graph/Data object containing the input
-            data
-        :type input: torch.Tensor or Graph or Data
-        :param conditional_variables: torch.Tensor or LabelTensor containing
-            the conditional variables
-        :type conditional_variables: torch.Tensor or LabelTensor
-        :return: DataCondition subclass
-        :rtype: TensorDataCondition or GraphDataCondition
         """
         if cls != DataCondition:
             return super().__new__(cls)
@@ -56,12 +59,15 @@ class DataCondition(ConditionInterface):
         Initialize the DataCondition, storing the input and conditional
         variables (if any).
 
-        :param input: torch.Tensor or Graph/Data object containing the input
-            data
+        :param input: Input data for the condition.
         :type input: torch.Tensor or Graph or Data
-        :param conditional_variables: torch.Tensor or LabelTensor containing
-            the conditional variables
+        :param conditional_variables: Conditional variables for the condition.
         :type conditional_variables: torch.Tensor or LabelTensor
+
+        .. note::
+            If either `input` is composed by a list of :class:`Graph`/
+            :class:`Data` objects, all elements must have the same structure
+            (keys and data types)
         """
         super().__init__()
         self.input = input
diff --git a/pina/condition/domain_equation_condition.py b/pina/condition/domain_equation_condition.py
index aad9d9f..58f9a66 100644
--- a/pina/condition/domain_equation_condition.py
+++ b/pina/condition/domain_equation_condition.py
@@ -20,9 +20,9 @@ class DomainEquationCondition(ConditionInterface):
         """
         Initialize the DomainEquationCondition, storing the domain and equation.
 
-        :param DomainInterface domain: Domain object containing the domain data
+        :param DomainInterface domain: Domain object containing the domain data.
         :param EquationInterface equation: Equation object containing the
-            equation data
+            equation data.
         """
         super().__init__()
         self.domain = domain
diff --git a/pina/condition/input_equation_condition.py b/pina/condition/input_equation_condition.py
index 9a267a3..0d0ebc7 100644
--- a/pina/condition/input_equation_condition.py
+++ b/pina/condition/input_equation_condition.py
@@ -22,15 +22,18 @@ class InputEquationCondition(ConditionInterface):
 
     def __new__(cls, input, equation):
         """
-        Instanciate the correct subclass of InputEquationCondition by checking
-        the type of the input data (only `input`).
+        Instantiate the appropriate subclass of InputEquationCondition based on
+        the type of input data.
 
-        :param input: torch.Tensor or Graph/Data object containing the input
-        :type input: torch.Tensor or Graph or Data
+        :param input: Input data. It can be a LabelTensor or a Graph object.
+        :type input: LabelTensor | Graph
         :param EquationInterface equation: Equation object containing the
-            equation function
-        :return: InputEquationCondition subclass
-        :rtype: InputTensorEquationCondition or InputGraphEquationCondition
+            equation function.
+        :return: Subclass of InputEquationCondition, based on the input type.
+        :rtype: InputTensorEquationCondition | InputGraphEquationCondition
+
+        :raises ValueError: If input is not of type :class:`torch.Tensor`,
+            :class:`LabelTensor`, :class:`Graph`, or :class:`Data`.
         """
 
         # If the class is already a subclass, return the instance
@@ -56,11 +59,18 @@ class InputEquationCondition(ConditionInterface):
         """
         Initialize the InputEquationCondition by storing the input and equation.
 
-        :param input: torch.Tensor or Graph/Data object containing the input
-        :type input: torch.Tensor or Graph or Data
+        :param input: torch.Tensor or Graph/Data object containing the input.
+        :type input: torch.Tensor | Graph
         :param EquationInterface equation: Equation object containing the
-            equation function
+            equation function.
+
+        .. note::
+            If ``input`` is composed by a list of :class:`Graph`/:class:`Data`
+            objects, all elements must have the same structure (keys and data
+            types). Moreover, at least one attribute must be a
+            :class:`LabelTensor`.
         """
+
         super().__init__()
         self.input = input
         self.equation = equation
@@ -90,11 +100,15 @@ class InputGraphEquationCondition(InputEquationCondition):
     @staticmethod
     def _check_label_tensor(input):
         """
-        Check if the input is a LabelTensor.
+        Check if at least one LabelTensor is present in the Graph object.
 
-        :param input: input data
+        :param input: Input data.
         :type input: torch.Tensor or Graph or Data
+
+        :raises ValueError: If the input data object does not contain at least
+            one LabelTensor.
         """
+
         # Store the fist element of the list/tuple if input is a list/tuple
         # it is anougth to check the first element because all elements must
         # have the same type and structure (already checked)
diff --git a/pina/condition/input_target_condition.py b/pina/condition/input_target_condition.py
index 70e09bc..b8d2dbf 100644
--- a/pina/condition/input_target_condition.py
+++ b/pina/condition/input_target_condition.py
@@ -21,17 +21,23 @@ class InputTargetCondition(ConditionInterface):
 
     def __new__(cls, input, target):
         """
-        Instanciate the correct subclass of InputTargetCondition by checking the
-        type of the input and target data.
+        Instantiate the appropriate subclass of InputTargetCondition based on
+        the types of input and target data.
 
-        :param input: torch.Tensor or Graph/Data object containing the input
-        :type input: torch.Tensor or Graph or Data
-        :param target: torch.Tensor or Graph/Data object containing the target
-        :type target: torch.Tensor or Graph or Data
-        :return: InputTargetCondition subclass
-        :rtype: TensorInputTensorTargetCondition or
-            TensorInputGraphTargetCondition or GraphInputTensorTargetCondition
-            or GraphInputGraphTargetCondition
+        :param input: Input data for the condition.
+        :type input: torch.Tensor | Graph | Data | list | tuple
+        :param target: Target data for the condition.
+            Graph, Data, or list/tuple.
+        :type target: torch.Tensor | Graph | Data | list | tuple
+        :return: Subclass of InputTargetCondition
+        :rtype: TensorInputTensorTargetCondition |
+            TensorInputGraphTargetCondition |
+            GraphInputTensorTargetCondition |
+            GraphInputGraphTargetCondition
+
+        :raises ValueError: If input and or target are not of type
+            :class:`torch.Tensor`, :class:`LabelTensor`, :class:`Graph`, or
+            :class:`Data`.
         """
         if cls != InputTargetCondition:
             return super().__new__(cls)
@@ -74,10 +80,16 @@ class InputTargetCondition(ConditionInterface):
         Initialize the InputTargetCondition, storing the input and target data.
 
         :param input: torch.Tensor or Graph/Data object containing the input
-        :type input: torch.Tensor or Graph or Data
+        :type input: torch.Tensor | Graph or Data
         :param target: torch.Tensor or Graph/Data object containing the target
         :type target: torch.Tensor or Graph or Data
+
+        .. note::
+            If either ``input`` or ``target`` are composed by a list of
+            :class:`Graph`/:class:`Data` objects, all elements must have the
+            same structure (keys and data types)
         """
+
         super().__init__()
         self._check_input_target_len(input, target)
         self.input = input
@@ -97,25 +109,27 @@ class InputTargetCondition(ConditionInterface):
 
 class TensorInputTensorTargetCondition(InputTargetCondition):
     """
-    InputTargetCondition subclass for torch.Tensor input and target data.
+    InputTargetCondition subclass for :class:`torch.Tensor`/:class:`LabelTensor`
+    input and target data.
     """
 
 
 class TensorInputGraphTargetCondition(InputTargetCondition):
     """
-    InputTargetCondition subclass for torch.Tensor input and Graph/Data target
-    data.
+    InputTargetCondition subclass for :class:`torch.Tensor`/:class:`LabelTensor`
+    input and :class:`Graph`/:class:`Data` target data.
     """
 
 
 class GraphInputTensorTargetCondition(InputTargetCondition):
     """
-    InputTargetCondition subclass for Graph/Data input and torch.Tensor target
-    data.
+    InputTargetCondition subclass for :class:`Graph`/:class:`Data` input and
+    :class:`torch.Tensor`/:class:`LabelTensor` target data.
     """
 
 
 class GraphInputGraphTargetCondition(InputTargetCondition):
     """
-    InputTargetCondition subclass for Graph/Data input and target data.
+    InputTargetCondition subclass for :class:`Graph`/:class:`Data` input and
+    target data.
     """