Charles Adam Platt (1861-1933) was an American architect and landscape designer. Although best remembered today for his landscape and country house designs, he was also nationally known for his etchings, landscape paintings, commercial architecture, and institutional projects. He was largely self-taught in each of these disciplines, building his success on his ability to reconceive the classical tradition in architecture for the needs and desires of his wealthy, powerful clients. This collection contains materials related to Platt's personal and professional lives, the bulk originating from Platt's office in the form of project drawings, photographs, and records documenting architectural projects from 1901-1933.

This collection contains architectural photographs, drawings and records related to the architectural projects and designs of Warren and Wetmore, principally in the United States, but also representing commissions in Canada, Cuba, and Puerto Rico. Unfortunately, the bulk of architectural drawings produced by the firm are no longer extant. Additionally, it holds a variety of photographs and other records used as reference materials in the course of Warren and Wetmore's professional work. Lastly, a small group of student and personal papers and photographs from Whitney Warren completes the collection.

Architectural plans and renderings of Welch's designs, largely New York City residences, circa 1890s-1920s; specifications; photographs; and brochures advertising buildings at 787 Fifth Ave., 628 Fifth Ave., and 71 and 73 Murray Street, in New York City. Drawings and a sketchbook done by Welch while a student; fourteen notebooks containing Welch's notes from Columbia classes in architecture, 1888-1890; licenses to practice in New York and New Jersey, 1904-1923; a certificate, 1937, and related correspondence relating to Welch's appointment as a U.S. delegate to the fourteenth International Congress of Architects, held in Paris, July 18-25, 1937. A list of U.S. delegates is included. Of note are drawings and papers for the restoration of the Dyckman House, an 18th century farmhouse in upper Manhattan (1910-1917); and the Mrs. Rutherford Stuyvesant Estate in Allamuchy, New Jersey, and the Rutherford Stuyvesant Momument in Tranquility Cemetery, Tranquility, New Jersey, designed by sculptor Daniel Chester French.

Alexander McMillan Welch (1869-1943) was a New York City based architect who practiced independently and as a member of Welch, Smith & Provot. His firm was best known for designing New York City townhouses in the Beaux-Arts style. The collection includes 1,641 architectural drawings, 196 student drawings, 14 student notebooks, 99 loose photographs and 3 photo albums of project photography, project specifications and files, and some professional ephemera.