This volume tries to continue a tradition of reviews of the contemporary research on the foundations of modern physics begun by the volume on the Einstein­ Podolsky-Rosen paradox that appeared a few years ago. (I) Its publication coin­ cides with the hundredth anniversary of de Broglie's birth (1892), a very welcome superposition, given the lasting influence of the Einstein-de Broglie conception of wave-particle duality. The present book, however, contains papers based on a broad spectrum of basic ideas, some even opposite to those that Einstein and de Broglie would have liked. The order of the contributions in this book is alphabetical by first author's name. It is important here to stress the presence of three reviews of fundamental experimental data, by Hasselbach (electron interferometry), Rauch (neutron interferometry), and Tonomura (Aharonov-Bohm effect). Hasselbach reviews several interesting experiments performed in 1Ubingen with the electron biprism interferometer. Wave-particle duality is brought out in striking ways, e. g. , in the buildup of an interference pattern out of single events. The Sagnac effect for electrons is also discussed. The chapter by Rauch presents interesting results on wave-particle duality for neutrons. Of particular interest are the differences between stochastic and deterministic absorption in the neutron interferometer, and the concrete evidence for the quantum-mechanical 41T-symmetry of spinors. In the short chapter by Tonomura, conclusive evidence for the reality of the Aharonov­ Bohm effect is reviewed, collected in experiments based on advanced technologies of electron holography and microlithography.