Koenig worked with Raphael Soriano and Edward H. Fickett among others, and began private practice in 1952. Koenig practiced mainly on the West Coast and was most notable for the design of the Case Study Houses No. 21 and 22 in 1960. Both 21 (the Bailey House) and 22 (the Stahl House) were constructed on dramatic, otherwise-unbuildable sites. Particularly the Case Study House #22, photographed by Julius Shulman, is widely considered the iconic postwar L.A. home, with its sweeping city views and openness to the outdoors.