These studies on the plankton of Tomales Bay were designed to determine the effects of such physical factors as tides, temperatures, salinities and sunshine on the quantities of various types of organisms, and to obtain a more comprehensive picture of estuarine life at the Pacific Marine Station. The studies were begun in the summer of 1948 and continued through the summer of 1953. Although various studies have been conducted on different aspects of marine plankton, the only general treatments of the subject of which the writer is aware are those of Johnstone (1924), Ricketts and Calvin (1951), Sproaton (1949) and Sverdup (19461). It is hoped that these additional studies will be of general interest to biologists and that they may form the basis for the solution of some of the many intriguing problems which have been encountered and are here presented in graphic form.