Book excerpt: The book presents an advanced but accessible overview of some of the most important sub-branches of magnetohydrodynamics (MHD): stability theory, magnetic topology, relaxation theory and magnetic reconnection. Although each of these subjects is often treated separately, in practical MHD applications they are normally inseparable. MHD is a highly active field of research.The book is written for advanced undergraduates, postgraduates and researchers working on MHD-related research in plasma physics and fluid dynamics.