On the occasion of W. Zimmermann's 70th birthday some eminent scientists gave review talks in honor of one of the great masters of quantum field theory. It was decided to write them up and publish them in this book, together with reprints of some seminal papers of the laureate. Thus, this volume deepens our understanding of anomalies, algebraic renormalization theory, axiomatic field theory and of much more while illuminating the past and present state of affairs and pointing to interesting problems for future research.