This book intends to give a systematic exposition of the validity of quantum principles in biological systems. There are two types of applications of quantum theory in physical systems the "trivial applications" and "non-trivial applications". Since every object in this universe consists of atoms and molecules, they should be described by the laws of quantum theory which we call trivial applications. On the other hand, there exist some systems where the observational results cannot be explained by the laws of classical physics and this requires a change of paradigm these are known as non-trivial applications. Many authors pointed out such non-trivial applications of quantum theory to explain how some biological systems function. In this book, we review such kinds of results in a systematic manner which clearly indicates the need to change the paradigm to understand these biological systems better.
