During and after World War II the Library of Congress held one of the largest collections of materials regarding sex and sexuality in the world. Largely composed of erotica and items considered to be pornographic or obscene, including books, motion pictures, photographs, and playing cards, the Library’s Delta Collection was separated from the general collection with highly restricted access. This collection was largely composed of materials seized by the Customs Bureau and the Postal Service, in addition to certain materials obtained through the Copyright Office, as the Library of Congress made the final decision regarding destruction, storage, and circulation of such items. The Delta Collection served to protect the materials from mutilation, preserve the cultural record, protect citizens from harmful obscenity, and function as a repository of sample materials for consultation by federal agencies. From evidence supplied by archival papers of the Keeper of the Collections, the office charged with maintaining the Delta Collection, this paper will show that an examination of LC policies and practices adds to our understanding of federal sexual politics and policing, particularly during the McCarthy era. The paper provides a narrative of the events that shaped the creation and maintenance of the Delta Collection and a discussion of its increased political significance during and after the war. It also offers an analysis of the use of the Delta symbol, which has origins in Greek mythology. The aim of is to shed light on the complexities of the Library of Congress’s role as a federal cultural institution in the control of sexually explicit materials.