The research material consists of Onsager's notes together with related reprints, manuscripts and correspondence. The folders are grouped in the following fourteen categories:
Dielectrics, Electrolytes, Ice, Irreversible processes, Thermal diffusion, Ising model, Metals and semiconductors, Liquid helium, Hydrodynamics, Surface tension, Origin of life, Mathematics, Colloids and Unclassified. The contents of each folder remain as Onsager left them.
In many cases, Onsager's own descriptions on the original folders or envelopes were transferred to the new folders by the Yale Library, and put in inverted commas. These often abbreviated Onsager labels have been extended to more complete titles (given in brackets). Some folders have comments on them, written by the researchers who were helping Yale University Library with the classification. The initials on the comments refer to Stefan Machlup (SM), Philip A. Lyons (PAL), John Nagle (JN), Raymond M. Fuoss (RMF) and Andrew Patterson, Jr. (AP).
5:1 Dielectric constant of hydrogen fluoride; 1972? SM