HERCULES is a course on the underlying principles and methods of neutron and synchrotron radiation techniques used in scientific research, constructed around laboratory practicals, tutorials and lectures and designed for biologists, chemists, geologists and physicists. This volume, the fourth in the HERCULES series, is the basis of the lecture course describing the theory and practice of techniques using either thermal neutrons or X- rays from a synchrotron source applied to the modern problems of biology. The themes treated are the crystallographic determination of protein structure, protein dynamics and partially ordered systems. A fourth section on more specialized topics includes spectroscopic techniques, X-ray microscopy, neutron spin polarization contrast methods and investigations of more complex molecules. Each chapter describes a different aspect of the subject, and the contributors are international authorities in their field. The book will be of use not only to beginners, but also, owing to the breadth of its scope, for experienced practitioners.