diff --git a/doc/source/pythonmodule.rst b/doc/source/pythonmodule.rst
index bc5e42a..11fa942 100644
--- a/doc/source/pythonmodule.rst
+++ b/doc/source/pythonmodule.rst
@@ -41,3 +41,13 @@ Timing
 .. autofunction:: time_block
 .. autofunction:: timeit
 .. autofunction:: timeit_quiet 
+
+
+Cosmology
+^^^^^^^^^
+
+Power spectrum
+--------------
+
+.. autoclass:: CosmologyPower
+   :members:
diff --git a/python/_cosmo_power.pyx b/python/_cosmo_power.pyx
index 4aebb15..b7b8334 100644
--- a/python/_cosmo_power.pyx
+++ b/python/_cosmo_power.pyx
@@ -49,11 +49,21 @@ cdef extern from "cosmopower.hpp" namespace "CosmoTool":
     double power(double)
  
 cdef class CosmologyPower:
+  """CosmologyPower(**cosmo)
+  
+  CosmologyPower manages and compute power spectra computation according to different
+  approximation given in the litterature.
+  
+  Keyword arguments:
+    omega_B_0 (float): relative baryon density
+    omega_M_0 (float): relative matter density
+    h (float): Hubble constant relative to 100 km/s/Mpc
+    ns (float): power law of the large scale inflation spectrum
+  """
 
   cdef CosmoPower power
 
-  def __init__(self,**cosmo):
-  
+  def __init__(self,**cosmo):    
     self.power = CosmoPower()
     self.power.OMEGA_B = cosmo['omega_B_0']
     self.power.OMEGA_C = cosmo['omega_M_0']-cosmo['omega_B_0']
@@ -66,11 +76,26 @@ cdef class CosmologyPower:
     self.power.updateCosmology()
     
   def normalize(self,s8):
+    """normalize(self, sigma8)
+    
+    Compute the normalization of the power spectrum using sigma8.
+    
+    Arguments:
+      sigma8 (float): standard deviation of density field smoothed at 8 Mpc/h
+    """
     self.power.SIGMA8 = s8
     self.power.normalize()
     
     
   def setFunction(self,funcname):
+    """setFunction(self, funcname)
+    
+    Choose an approximation to use for the computation of the power spectrum
+    
+    Arguments:
+      funcname (str): the name of the approximation. It can be either
+                      EFSTATHIOU, HU_WIGGLES, HU_BARYON, BARDEEN or SUGIYAMA.
+    """
     cdef CosmoFunction f
     
     f = POWER_EFSTATHIOU
@@ -93,6 +118,19 @@ cdef class CosmologyPower:
     return self.power.power(k)
     
   def compute(self, k):
+    """compute(self, k)
+    
+    Compute the power spectrum for mode which length k.
+    
+    Arguments:
+      k (float): Mode for which to evaluate the power spectrum.
+                 It can be a scalar or a numpy array. 
+                 The units must be in 'h Mpc^{-1}'.
+    
+    Returns:
+      a scalar or a numpy array depending on the type of the k argument 
+    """
+    
     cdef np.ndarray out
     cdef double kval
     cdef tuple i