Preface. Introduction: 1. Factors in the development of modern physics (A. Sarlemijn, P.A. Kroes, F.W. Sluijter and M.J. Sparnaay). Part I: Historical Examples of Physics in the Making. 2. Physics in the making in Leiden - Paul Ehrenfest as teacher (M.J. Klein). 3. Physics in the making in Bohr's Copenhagen (A. Pais). 4. Physics in the making in Pauli's Zürich (K. von Meyenn). Part II: Theoretical and Experimental Physics: Reports on Recent Developments. 5. The physical concept of time in the 20th century (P.T. Landsberg). 6. Statistical foundations of electrodynamic theory (L.G. Suttorp). 7. The role of Onsager relations in the development of thermodynamics of irreversible processes (P. Mazur). 8. Dynamic symmetries and supersymmetries in nuclear and particle physics (F. Iachello). 9. The Casimir effect - 9.A. Historical background of the Casimir effect (M.J. Sparnaay). 9.B. The Casimir effect in field theory (B. DeWitt). Part III: Physics in Industrial Laboratories. 10. The development of fluorescent lamps at Philips up to 1940 (J.J. Hutter). 11. Approaches to science in industry (K.A. Müller). Part IV: Reflexions on Physics in the Making. Fundamental laws and physical reality (P.A. Kroes and A. Sarlemijn). 13. A philosophy of physics in the making (C.F. von Weizsäcker). Appendix - Casimir's teachings in Leiden and in Eindhoven (C.M. Hargreaves).