In this collection the letters of some 946 authors present a history of American entomology and especially of the American Entomological Society and the Entomological section of the Academy. Under discussion are the society affairs, working funds, publications and scientific courtesies, exchanges with other museums and entomologists. The recipients appear to be primarily the secretaries and recorders of the two organizations mentioned. Collections received at three different times from the Department of Insects are combined and treated as a unit. The Historical file supervised by E. T. Cresson, Sr. and continued by his son of the same name were transfered to the library of the Academy in 1948 for safe-keeping. Another series of letters belonging to the Society but preserved in the Department was referred to the Academy's library in 1960 by S. S. Roback, corresponding secretary. The third group was removed from an old scrapbook of the Society and contains much of the earlier correspondence included here. A large number of carbon answers and manuscript transcriptions of replies have been included but not counted in the series.