The book provides the background needed for fundamental concepts in biophysics. Biophysics is a bridge between biology and physics, the study of biological systems and biological processes using physics-based methods or based on physical principles. Biology studies life in its variety and complexity. It describes how organisms go about getting food, communicating, sensing the environment, and reproducing. Biophysics is a molecular science that seeks to explain biological function in terms of the molecular structures and properties of specific molecules. An important area of biophysical study is the detailed analysis of the structure of molecules in living systems. The best-known achievement related to this area is the model of deoxyribonucleic acid (DNA), the hereditary material of life.