The essential topics in the field of sexual dimorphism are elaborated in this book. There have been several studies which describe sex differences in humans as well as in mammals, birds, amphibians, insects extending up to even ostracoda of the Paleozoic era by applying novel approaches and innovative methodologies. This book provides logical and vivid insights into the evolution of sex differences. It also explains how living beings that may not seem to have sex differences, possess some characteristics which indicate otherwise. The book provides unique perspectives and intriguing viewpoints on the subject of sex differences and aims to assist biologists, life scientists, social and cultural scientists in their study and research on sexual dimorphism.