The collection includes Lejewski's manuscript notes and formulae created during his research together with drafts and typescripts of his published works. It contains typescript drafts and reprints of articles by various scholars, particularly philosophers, and published copies of philosophy journals. There are many papers by, or about, the Polish mathematician and philosopher Stansiław Leśniewski who was one of Lejewski's teachers. In some of the articles authored by Lejewski he explores and advances Leśniewski's ideas in logic. The collection also includes Lejewski's correspondence with Professor Bolesław Sobociński and others.
Donated to Special Collections by his widow, Joan Lejewska, through the agency of Professor Peter Simons, in 2007.