This book gives a concise description of the phenomenon of plasma relaxation from the point of view of resistive magnetohydrodynamic (MHD) theory. Magnetized plasmas relax when they seek their natural state of lowest energy subject to certain topological constraints imposed by the magnetic field. Relaxation may be fast and dynamic or slow and gradual depending on the external environment in which the magnetoplasma system evolves. Relaxation occurs throughout the universe and may describe such diverse phenomena as dynamos, solar flares, and the operation of magnetic fusion energy experiments. This book concentrates on the dynamics, rather than variational aspects of relaxation. While the processes described are general, the book focuses on the reversed-field pinch experiment as a paradigm for plasma relaxation and dynamo action. Examples from other branches of plasma physics are also discussed. The authors draw upon their extensive experience in numerical and experimental studies of relaxation.