On November 12-14, 1997 a workshop was held at the Vrije Universiteit Amsterdam on the occasion of the sixtieth birthday ofM. A. Kaashoek. The present volume contains the proceedings of this workshop. The workshop was attended by 44 participants from all over the world: partici pants came from Austria, Belgium, Canada, Germany, Ireland, Israel, Italy, The Netherlands, South Africa, Switzerland, Ukraine and the USA. The atmosphere at the workshop was very warm and friendly. There where 21 plenary lectures, and each lecture was followed by a lively discussion. The workshop was supported by: the Vakgroep Wiskunde of the Vrije Univer siteit, the department of Mathematics and Computer Science of the Vrije Univer siteit, the Stichting VU Computer Science & Mathematics Research Centre, the Thomas Stieltjes Institute for Mathematics, and the department of Economics of the Erasmus University Rotterdam. The organizers would like to take this opportunity to express their gratitude for the support. Without it the workshop would not have been so successful as it was. Table of Contents Preface … … … … … … … … … … … … … … … … … … … … … . v Photograph of M. A. Kaashoek … … … … … … … … … … … … … . . xiii Curriculum Vitae of M. A. Kaashoek … … … … … … … … … … … … xv List of Publications of M. A. Kaashoek … … … … … … … … … … … xix l. Gohberg Opening Address … … … … … … … … … … … … … … … … … xxxi H. Bart, A. C. M. Ran and H. I. Woerdeman Personal Reminiscences … … … … … … … … … … … … … … . . xxxv V. Adamyan and R. Mennicken On the Separation of Certain Spectral Components of Selfadjoint Operator Matrices … … … … … … … … … … … … . . 1 1. Introduction … … … … … … … … … … … … … … … 1 2. Conditions for the Separation of Spectral Components … … . 4 3. Example … … … … … … … … … … … … … … … … 9 References … … … … … … … … … … … … … … … …