The collection consists of group portraits and other photos of Princeton University classes. Though some photographs depict the classes while their members were students, the majority of the photographs are from alumni reunions.

The Grounds and Buildings Series of the Historical Photograph Collection contains photographs of the grounds and buildings owned by Princeton University. The photographs date from the late 1850s to the present, with the bulk of the photographs dating from the 1870s to the 1940s. Many of these photographs have been digitized and are searchable in Digital PUL.

The Historical Photograph Collection: Individuals series consists of photographs of faculty, administration, trustees, staff, students, and notable visitors to Princeton University.

Consists of several hundred lantern slides containing images of Princeton University, primarily the campus and buildings.

The Student Photograph Albums Series of the Historical Photograph Collection (HPC) contains 180 photographic albums created by Princeton University students. These albums, along with the other photograph collections in the University Archives, help document the experiences of students, faculty, and staff at Princeton University. The albums date from 1851 to 1995, although the bulk date from the 1860s to the 1910s. New accessions are added regularly to the collection.

The Historical Postcard Collection documents the buildings and environs of the Princeton University campus in the form of picture postcards. Featuring both monochrome and color postcards, the bulk of the collection ranges in date from 1900 through the 1960s. Many of the postcards have been digitized and are searchable through Digital PUL.

The Historical Subject Files Collection documents Princeton University history and related topics from 1746 to the present. The collection consists of documents in almost every two-dimensional format: articles, books and booklets, clippings, correspondence, memoranda, non-photographic images, notes, pamphlets, posters, and reports.

Files include correspondence about the founding of Princeton University Libray's William Seymour Theatre Collection, the gala dinner opening night, efforts to enlarge the collection in the 1940 to 1960s, and descriptive writings about the collection by the various curators.

Consists primarily of microfilm and transcripts of letters by American essayist and journalist H. L. Mencken, compiled by Princeton University historian and librarian Julian Boyd for his proposed book of Mencken's letters.

Consists of 108 letters by Mencken to Dent Smith between the years 1938 and 1945, with Smith's side of the correspondence present in carbon copies.