Personal and professional papers of the planetary astronomer who discovered Pluto in 1930. Personal papers document Tombaugh's Kansas boyhood, his early interest in astronomy and telescope making, and his arrival at Lowell Observatory, Flagstaff, Arizona, in 1929. Later materials concern his diverse interests in politics, education, and religion, and his family life. The extensive professional papers span Tombaugh's full career, from his observational work at Lowell to his tenure at New Mexico State University (NMSU). Tombaugh's employment at the White Sands Proving Ground (1946-1955) and his research in optics are included. The Near Earth Satellite Search, a study initiated by Tombaugh at White Sands and continued during his subsequent employment at NMSU is thoroughly documented. The bulk of the professional papers concern his employment at NMSU (1955-1973) and his work with the Planetary Patrol and Study Project. Records also illustrate the development of the NMSU Department of Astronomy. Correspondence with prominent professional and amateur astronomers, astrophysicists, and experts in related sciences is found throughout the collection, as are such visual materials as drawings, photographs, and maps.