Allan Stevenson & Cassels was an early 20th century architectural practice in Scotland.
The company, a partnership originally between Allan Stevenson and Thomas McGill Cassels, was first active, under that name, from around 1922 to 1927.
Stevenson died around 1923, and in 1927 Cassels merged the practice with that of Stevenson's former apprentice, Alexander Mair. The company became Allan Stevenson, Mair and Cassels.
The company reverted to the original name of Allan Stevenson & Cassels in 1929 with Mair's departure.
Cassels continued the practice alone until 1945. At this point, the company was taken over by Duncan McCulloch. It was later taken over by E A Darley and became known as the Darley Hay Partnership.