Book excerpt: Interested in analysing complex systems? Have you considered nuclear magnetic relaxation studies to derive sound conclusions? Here’s how. Nuclear Magnetic Resonance (NMR) relaxation techniques form a family of powerful tools to study and characterize liquid, solid or semi-solid materials and systems. They provide access to details directly and in wide variable ranges. This book outlines the unparalleled potential of NMR relaxation experiments to elucidate molecular dynamics. The key concepts discussed are correlation functions and spectral densities of the thermal fluctuations of spin interactions. For users working in technology, chemical engineering, materials science, biomedicine, food science, geophysics and physical chemistry, the text explores the principles, theoretical background and descriptions of typical applications. As an essential part of relaxation data, the focus is on the statistical features of molecular dynamics. The aim is to assist the reader to acquire meaningful nuclear magnetic relaxation data sets and develop appropriate statistical models as a basis for their interpretation. This unique text is targeted to anyone performing or interested in NMR relaxation experiments from undergraduates to academics and those in industry.