This book attempts to give the non-specialist reader a general view of what physicists do, and of the problems which are still to be solved in contemporary physics. In contrast to many popular books on the subject, it concentrates not on the achievements of physicists, but on the exciting frontier areas of modern physics, and the fascinating work which is still to be done in the field. Readership: sixth-formers planning to study physics at a higher level; first-year physics students and academics in related disciplines; some general readers with a particular interest in physics.