This revised and enlarged fourth edition features five new chapters, which treat classical results such as the 'Fundamental Theorem of Algebra', problems about tilings, but also quite recent proofs, for example of the Kneser conjecture in graph theory. The new edition also presents further improvements and surprises, among them a new proof for 'Hilbert's Third Problem'. From the Reviews: '... Inside [this book] is indeed a glimpse of mathematical heaven, where clever insights and beautiful ideas combine in astonishing and glorious ways. There is vast wealth within its pages, one gem after another. ..., but many [proofs] are new and brilliant proofs of classical results. ...Aigner and Ziegler... write: '... all we offer is the examples that we have selected, hoping that our readers will share our enthusiasm about brilliant ideas, clever insights and wonderful observations.' I do. ... ' AMS Notices 1999 '... the level is close to elementary ... the proofs are brilliant. ...' LMS Newsletter 1999