Solvay conferences aim to have two main characteristics. In planning them, our Scientific Council first chooses a unifying theme to link together diversified lines of scientific research, in which recent advances have been rapid. Leading scientists concerned with these advances are then invited from all over the world to Brussels, to present their successes—and their difficulties—to one another and to a small audience also specially invited. As is well known, spearhead advances in modern science must concentrate their attack on a fairly narrow front to make effective progress. But this very concentration often leads to a spread of advances in widely separated directions, like the fingers of a starfish. Those moving along one finger of the star can be wastefully ignorant about the other fingers. At Solvay conferences, by bringing experts in different lines together, our purpose is to encourage cross-communication of suggestive ideas and to promote mutual borrowing of scientific techniques. Measured by size, compared with very large scientific conferences now organized all over the world, Solvay conferences remain an “elitist” mode of scientific communication, in the sense that the number of invited experts is deliberately kept rather small, and that abundant time is provided for discussions. Discussion proceedings are fully recorded and their subsequent publication in book form is of course read by a much greater number of scientists afterwards.