Book excerpt: Biophysics is the science of physical principles underlying the "phenomenon of life" on all levels of organization. This book begins by explaining molecular and ionic interactions, movements, excitation and energy transfer, and the self-organization of supramolecular structures. Then the biological organism is introduced as a non-equilibrium system. Finally, system analyses are discussed as well as environmental biophysics, ecological interactions, growth, differentiation, and evolution. A growing number of applications in biotechnology are based on these biophysical concepts.