The Architects Collaborative (TAC) was an American architectural firm formed by eight architects that operated between 1945 and 1995 in Cambridge, Massachusetts. The founding members were Norman C. Fletcher (1917–2007), Jean B. Fletcher (1915–1965), John C. Harkness (1916–2016), Sarah P. Harkness (1914–2013), Robert S. McMillan (1916–2001), Louis A. McMillen (1916–1998), Benjamin C. Thompson (1918–2002), and Walter Gropius (1883–1969). TAC created many successful projects, and was well respected for its broad range of designs, being considered one of the most notable firms in post-war modernism.

Norman Fletcher, Louis McMillen, Robert McMillan, and Ben Thompson first laid the conceptual foundation for what became the Architects Collaborative while they were classmates at Yale University, where they discussed forming "the World Collaborative", which would be an ideal office combining painting, sculpture, and architecture.

Upon graduation, Norman Fletcher worked with John Harkness during the war at Skidmore, Owings & Merrill in New York, and later, John Harkness worked with Jean Fletcher for Saarinen and Swanson in Bloomfield Hills, Michigan. Jean Fletcher and Sarah Harkness had both studied at the Cambridge School of Architecture and Landscape Architecture.

This group of friends were committed to forming a collaborative practice. To help them navigate the professional world and lend notability to the firm, they sought to add a senior practitioner. John Harkness pitched the idea of joining the Architects' Collaborative to Walter Gropius, who had asked Harkness to teach a master's class at Harvard. Gropius agreed and became the eighth member of the group. Other principals came to include Richard Brooker, Alex Cvijanović, Herbert Gallagher, William Geddis, Roland Kluver, Peter Morton and H. Morse Payne Jr.

The idea of collaboration was the basis of TAC. In the book about TAC she co-authored with Gropius, Sarah Harkness wrote that "There are two ways to go--towards competition or towards collaboration. A contest can be stimulating, but as a way of life competition is wasteful."

In a 2023 interview, Perry Neubauer who joined the firm in 1965, said "It was a different ballgame when I came up to Cambridge and worked at TAC. We would sit in a design meeting and grab the pencil out of each other’s hands. ”Hey, what do you think about this?” Anybody could say anything. You weren't going to dispute things with Gropius, probably, But everyone thought they could offer an opinion. That was the strength of TAC."

As described by McMillen, conforming to the ideal of anonymity helped bind the office together. It was carried out in that an entire group of architects have their input on a project, rather than putting an emphasis on individualism. There would be a "partner-in-charge", who would meet with clients and have the final decision of what goes into the design. Originally, each of the eight partners would hold weekly meetings on a Thursday to discuss their projects and be open to design input and ideas. However, as the firm grew larger there were many more people on a team and it was more difficult to consolidate into one group. Therefore, many other "groups" of architects within the firm were formed and carried out the same original objective. The position of the firm's president would be rotated amongst the senior partners.

TAC's initial work consisted of residential projects, mainly single-family houses. The most notable design was Six Moon Hill in Lexington, Massachusetts, a community dwelling in which several of the houses were the residences of the founding partners, excluding Gropius. Another one of TAC's specialties in this period was school buildings, which included many elementary and secondary public schools throughout Massachusetts and New England. TAC also designed many buildings for universities, among which was the Harvard Graduate Center, a small campus of dormitories and a building devoted to student activities.