diff --git a/icartt/dataset.py b/icartt/dataset.py
index 0ae68fc0b372af47e565750782a75f8510609882..3d64ad6ac539ce23be97295b460218683cd987c8 100644
--- a/icartt/dataset.py
+++ b/icartt/dataset.py
@@ -2,6 +2,9 @@ import datetime
 import sys
 
 class Variable:
+    '''
+    A Variable is a full ICARTT variable with name, units, scale and missing value.
+    '''
     @property
     def desc(self):
         return self.splitChar.join( [self.name, self.units, self.units ] )
@@ -12,6 +15,10 @@ class Variable:
         self.miss = str(miss)
 
 class Dataset:
+    '''
+    An ICARTT dataset that can be created from scratch or read from a file,
+    manipulated, and then written to a file.
+    '''
     @property
     def nheader(self):
         total = 12 + self.ndvar + 1 + self.nscom + 1 + self.nncom