This Catalog originated as a common enterprise of solar physicists and space scientists under the auspices of the Second Working Group of the Inter-Union Commission of Solar Terrestrial Physics (IUCSTP). It is a pleasure to acknowledge the support we received from the IUCSTP president, Dr H. Friedman, and the IUCSTPSecretary, Dr E. R. Dyer during the several years we have spent on this project. The aim of our work has been to assemble all observations of particle events from the first PCA observation in 1955 through two solar cycle maxima up to the end of 1969, in order to preserve these data...