TheReviews of Modern Physicsstarted as Physical Review Supplement in July, 1929. It has developed, in the 27 years since its foundation, into one of the most important sources of information for physicists. The need for a review journal which summarizes recent progress and trends in certain parts of physics, for the benefit of those whose principal interest and preoccupation is in other fields, must have been evident to its first editorial board which, included John T. Tate, A. H. Compton, K. T. Compton, K. K. Darrow, E. C. Kemble, C. E. Mendenhall, and D. L. Webster. Today, the unprecedented growth of the volume of publications renders such a journal a necessity. Without journals such as theRMP, our special interests would make our knowledge of the various branches of physics even more oppressively narrow than most of us feel it already is. This writer, for one, derives practically all his acquaintance with radio‐astronomy, with the theories of earth magnetism, with magneto‐hydrodynamics, from articles in theReviews of Modern Physics, and he suspects that the majority of his colleagues could present a similar list.