Cochin Backwaters situated at the tip of Northern Vembanad lake is a tropical positive estuarine system in Kerala, India. During South West monsoon it is virtually converted to fresh water basin and the salinity gradient support diverse species of flora and fauna according to their tolerance for saline environment. Benthic fauna is of considerable importance in Marine food chain. Benthic fauna also serve as good indicator species and are widely employed in pollution monitoring. This book investigates and compares the occurrence, abundance and distribution of major groups of macro benthic fauna in Cochin Back waters during the monsoon and post monsoon season.