This, the fourth edition of Stuwe's book on the calculus of variations,
surveys new developments in this exciting field. It also gives a concise
introduction to variational methods. In particular it includes the proof
for the convergence of the Yamabe flow and a detailed treatment of the
phenomenon of blow-up. Recently discovered results for backward bubbling
in the heat flow for harmonic maps or surfaces are discussed. A number
of changes have been made throughout the text.