Biology is a natural science that is concerned with the study of living organisms and the organization of life at chemical, molecular, physical and physiological levels. Cell theory, genetics, homeostasis, evolution and energy provide the theoretical foundations of biology. Biology is a vast discipline that differentiates into a number of significant sub-disciplines such as anatomy, biochemistry, biological engineering, biophysics, botany, zoology, developmental biology, ecology, evolutionary biology, genetics, marine biology, etc. This book is compiled in such a manner, that it will provide in-depth knowledge about the principles and applications of biology. Such selected concepts that redefine this discipline have been presented herein. This book is an essential guide for both academicians and those who wish to pursue this discipline further.