Mancini Duffy (stylized as Mancini•Duffy) is a New York City-based architecture and interior design firm.

The firm provides a full range of interior planning, design, and architecture services as well as specialized services such as CAFM, strategic planning, and workplace strategy; graphics and signage; identity and brand development; and product design.

Originally established in 1915 as Thomas Bruce Boyd Architect, Inc., the corporation reorganized in 1920 and changed its name to Halsey, McCormack & Helmer, Inc.[1] The firm was noted for its prestigious banking projects, including the Williamsburgh Savings Bank Tower in Brooklyn, New York; it was purchased by Duffy Inc. in 1967.

High-profile projects include headquarters relocations for JPMorgan Chase, CIT Group, Condé Nast Publications, and AOL; a headquarters build-out for Time Warner at Time Warner Center; new television studios and production facilities for NBC Sports Group in Stamford, CT; and an ongoing renovation of Bloomingdale's flagship store in Manhattan.

[2] A former tenant of Two World Trade Center, Mancini Duffy's New York offices were destroyed in the September 11 attacks.