diff --git a/phasecalculator/classes/phases.py b/phasecalculator/classes/phases.py
index 2a164b5943fad9757b6d4e938ce484cb17296103..6b5a86fd35e4a645fb0c8816c862d3123250015e 100755
--- a/phasecalculator/classes/phases.py
+++ b/phasecalculator/classes/phases.py
@@ -33,6 +33,18 @@ class Phases(object):
     """Phases class."""
 
     def __init__(self, phase_list):
+        """Initialise Phases.
+
+        Parameters
+        ----------
+        phase_list : list of Phase objects.
+            Phases for calculation.
+
+        Returns
+        -------
+        New Phases Instance.
+
+        """
         self.phase_list = phase_list
         
     def __eq__(self, other):
diff --git a/phasecalculator/classes/system.py b/phasecalculator/classes/system.py
index df84650807717387542ce477e4cd0d41a8138ca1..56b8369715a6c2cc5b8dee16ad41425fe98e28ca 100755
--- a/phasecalculator/classes/system.py
+++ b/phasecalculator/classes/system.py
@@ -36,6 +36,18 @@ LOGGER.setLevel(logging.WARN)
 class SystemCollection(object):
     """System Collection class."""
     def __init__(self, system_list):
+        """
+
+        Parameters
+        ----------
+        system_list : list of System
+            List of systems.
+
+        Returns
+        -------
+        None.
+
+        """
         self.system_list = system_list
     def __eq__(self, other):
         """Overload equality comparison operator.
@@ -95,6 +107,22 @@ class SystemCollection(object):
 class System(object):
     """System class"""
     def __init__(self, phases, runtime_information, output_information):
+        """Initialise new System.
+
+        Parameters
+        ----------
+        phases : Phases
+            Phases of interest.
+        runtime_information : RuntimeInformation
+            Runtime parameter information.
+        output_information : OutputInformation
+            Output option information.
+
+        Returns
+        -------
+        None.
+
+        """
         self.phases = phases
         self.runtime_information = runtime_information
         self.output_information = output_information