While in Italy on a Fulbright Scholarship in 1954, Diffrient went to work in the studio of the great architect Marco Zanuso, where he assisted with the design of an award-winning Borletti sewing machine.

Upon arriving back in the United States in 1955, Diffrient joined Dreyfuss Associates in their Pasadena offices, and spent the next few decades revolutionizing American industrial design through his development of interiors and corporate identity for American Airlines planes, the landmark Princess telephone, the Polaroid SX-70 camera, and tractor operator cabs for John Deere.

[2] In 1980 after 25 years with Henry Dreyfuss Associates, Diffrient left to start his own independent practice, establishing a design studio in Ridgefield, Connecticut which he shared with his second wife, tapestry artist Helena Hernmarck.

[3] In his career, which lasted over a half century, Diffrient designed every type of equipment, as well as computers, exhibits, trucks, airplane interiors and corporate identity programs.

[9][10][11] Chairs: Humanscale also manufactures keyboard support systems, monitor arms, task lighting, and various other ergonomic work tools,[9] including: