The Joseph Leidy Correspondence Collection contains letters from scholars, scientists and acquaintances to Joseph Leidy with a few letters from Leidy to various correspondents. Many of the correspondents were associated with the natural sciences, medicine and acadamia. The letters discuss travel, field work, research, theories, finances, and personal lives and reflect his wide interest in all phases of natural history, protozoology, embryology, parasitology, paleontology, anthropology, mineralogy and botany. According to the "Guide to the Manuscript Collections in the Academy of Natural Sciences" (1962) this collection of correspondence consists of 2700 items written by approximately 800 scientists including a small collection of letters written by Leidy. Noted or extensive correspondents include Ferdinand V. Hayden, S.F. Baid, Charles Darwin, and Flinders Petrie.

The letters are organized alphabetically according the last name of the writer. Letters by the same author are organized chronologically.