H.B.G. Casimir's life, interests and works are intertwined with the importantdevelopments that have taken place in physics during this century. This book was compiled by his friends and admirers in honour of his 80th birthday andconcentrates mainly on Casimir's achievements in the field of physics, thoughwithout ignoring the peripheral areas of the history and philosophy of physics in which he was greatly interested. The book is divided into four parts. Part I describes Casimir's teachers, Ehrenfest, Bohr and Pauli, and will be of general interest due to the key role which these physicists played in moderndevelopments. The articles do give new facts and provide new insights into thehistory of modern physics. Part II consists of essays on recent developments invarious areas of physics in which Casimir has taken an active interest, such asthe modern concept of time, statistical foundations of electrodynamic theory andfield theory. The subjects covered in Part III have been selected because ofCasimir's efforts in the industrial research area of physics. They cover past,present and future expectations in research. Part IV contains an essay whichdiscusses a philosophy of physics currently under discussion, which states thatphenomenological laws prevail over fundamental ones for the purpose ofexperimental and technical physics. A second chapter in this final part gives acritical analysis of this philosophical view. The book is concluded by anappendix discussing Casimir's activities as a lecturer, written by a formerstudent.