The correspondence that appears here is a complete set of all known letters between Japanese and other researchers and the Lederbergs (Esther and Joshua) found in the Esther M. Zimmer Lederberg archive. All but one of these letters are dated between 1961 and 1964. In most cases, only Esther M. Lederberg is addressed. In a few cases, letters are addressed to both of the Lederbergs; however, in all cases only Esther initiates or responds. Even where pre-printed forms with Joshua's name on them are used, as stated the only signature that appears appears is Esther's.

This collection of correspondence is named "Japanese Correspondence" because all the researchers either lived primarily in Japan, or were primarily associated with Japanese Universities or research institutes. Esher Lederberg met most of these researchers during her trip to Japan in 1962. (Dr. Y. Hirota did work as a researcher at the Lederbergs' laboraory in Wisconsin, but Dr. Hirota also did much resaearch in Japan.)