Two important events in the history of physical sciences occurred re cently: the fiftieth anniversary of Quantum Mechanics and the Jubilee of Louis de Broglie's celebrated Thesis. These events occurred in the same period of time when the world honored de Broglie on the occa sion of his eightieth birthday. Some of de Broglie's friends, former students, and some people who used to know him and appreciate his personality decided to prepare an international volume for this cele brated occasion. Such a task was not very easy. It is always simpler to contribute in honor of famous people whose works...