This book contains the proceedings of the international workshop organized at the Vrije Universiteit Amsterdam in November 1997 and dedicated to the sixtieth birthday of M.A. Kaashoek, one of the leading experts in operator theory and its applications. The workshop focused on areas in mathematical and functional analysis where the ideas and results of M.A. Kaashoek played an important role. The papers of this volume cover a wide range of topics centered around factorization of matrix valued functions, interpolation theory, and spectral theory. Other papers deal with canonical systems of differential equations, operators in indefinite inner product spaces, and the effect of small delays on stability and control of partial differential equations. The book starts with biographical material and a list of publications of M.A. Kaashoek. The main part consists of original research papers, which contain new interesting results. The book will be of interest to a wide range of readers in pure and applied mathematics and engineering.