This volume of the series Biophysics for the Life Sciences focuses on the conceptual framework and major research tools of contemporary molecular biophysics. It is designed to enable non-specialists -both students and professionals in other fields - to understand how these approaches can be used across the biosciences and in medicine, agriculture, biotechnology, pharmaceutical development and other fields. The scope of this volume is appropriate for advanced undergraduate and graduate courses in biophysics and biophysical chemistry. The book begins with an overview of the development of molecular biophysics and a brief survey of structural, physical, and chemical principles. Subsequent chapters written by experts present, with examples, the major experimental methods: optical spectroscopy, X-ray and neutron diffraction and scattering, nuclear magnetic resonance, electron paramagnetic resonance, mass spectrometry, and single molecule methods. The relationship between the biophysical properties of biological macromolecules and their roles as molecular machines is emphasized throughout and illustrated with three examples DNA helicases, rotary motor ATPases, and myosin. The concluding chapter discusses future prospects in X-ray and neutron scattering, mass spectrometry, and pharmaceutical development