The word “bionomic” has been originated from two Greek words, i.e., “bio” meaning “life” and “nomos” meaning “law.” In general, it is the comprehensive study of an organism along with its relationship with the environment. To study bionomics of parasites, we must concentrate their physiology encompassing their nutrition, metabolism, circulation, excretion, reproduction, etc. In this chapter, all have been briefly described so that a reader can have an overview about some physiological and biochemical aspect.