Entities
- Café du Dôme <Paris>
- Letter from: 16.1.1929, Paris (France)
- Café du Paris <Monte Carlo>
- Letter from: 9.1.1929, Monte-Carlo (Monaco)
- Café La Coupole <New York>
- Letter from: 16.10.1949, New York
- Café Niedlich <Allenstein>
- Letter from: 13.6.1920, Allenstein (Germany)
- Café Royal <London>
- Letter from: 29.6.1939, London
- Café Stark <Allenstein>
- Letter from: 21.6.1920, Allenstein (Germany)
- Canadian Pacific Railway
- Letter from: 20.9.1955, auf der Reise nach Toronto (Canada)
- Cantorowitzsche Stube <Berlin>
- Letter from: 18.10.1918, Charlottenburg (Berlin;Germany)
- Cap-Martin Hotel <Menton>
- Letter from: 8.1.1929, Menton / Alpes-Maritimes (France)
- Letter from: 10.1.1929, Cap Martin / Alpes-Maritimes (France)
- Capital Airlines
- Letter from: 19.10.1949, Auf dem Flug von New York über Pittsburgh nach Saint Louis
- Letter from: 27.1.1950, Grand Rapids
- Capitol <Washington, D.C.>
- Letter from: 4.7.1947, Washington
- Cargo Ltd. <San Francisco?>
- Letter from: 22.1.1948, San Francisco (Calif.)
- Carmel Inn <Carmel, Kalifornien>
- Letter from: 3.6.1952, Maui (Hawaii)
- Carnegie Art Institute <Pittsburgh>
- Letter from: 22.10.1924, Pittsburgh
- Carolina Inn <Chapel Hill>
- Letter from: 6.2.1950, Chapel Hill
- Casino <Monte Carlo>
- Letter from: 9.1.1929, Monte-Carlo (Monaco)
- Letter from: 10.1.1929, Cap Martin / Alpes-Maritimes (France)
- Ceylon-Teestube <München>
- Letter from: 15.7.1913, Munich (Germany)
- Letter from: 26.11.1913, München
- Chamber of Commerce <Saint Louis, Missouri>
- Letter from: 14.3.1944, Saint Louis
- Chamber of Commerce <San Francisco>
- Letter from: 30.4.1942, San Francisco
- Letter from: 6.11.1945, San Francisco
- Chase Hotel <Saint Louis, Missouri>
- Letter from: 16.6.1945, Saint Louis
- Letter from: 9.12.1945, Saint Louis
- Letter from: 2.3.1946, Saint Louis
- Letter from: 3.5.1947, Saint Louis
- Letter from: 26.6.1950, Saint Louis
- Chocoladefabriken Lindt & Sprüngli
- Letter from: 14.7.1925, Saint Moritz (Switzerland)
- Church of England
- Letter from: 27.4.1938, London (England)
- City Ballet <New York>
- Letter from: 22.12.1952, New York (N.Y.)
- City Club Berlin
- Letter from: 9.9.1932, Berlin-Spandau
- City Temple <London>
- Letter from: 23.4.1938, London (England)
- Letter from: 27.4.1938, London (England)
- Clairmont <San Francisco>
- Letter from: 25.1.1948, San Francisco (Calif.)
- Letter from: 28.1.1948 [?], San Francisco (Calif.)
- Claridge's Hotel <London>
- Cleveland Museum <Cleveland, Ohio>
- Letter from: 24.4.1947, Cleveland
- Cliff Dwellers Club <Chicago>
- Letter from: 27.1.1950, Grand Rapids
- Cliff House <San Francisco>
- Letter from: 1.11.1945, San Francisco
- Coburger Hütte <Tirol>
- Letter from: 21.8.1917, Oberammergau (Germany)
- Colonial office <Jerusalem>
- Letter from: 3.7.1939, Jerusalem
- Columbia University
- Letter from: 7.12.1941, New York (N.Y.)
- Letter from: 21.4.1942, San Francisco
- Letter from: 28.4.1942, Croton-on-Hudson (N.Y.)
- Letter from: 17.12.1952, New York (N.Y.)
- Columbia University, School of Architecture <New York>
- Letter from: 30.4.1947, Washington
- Comologno <Palazzo della Barca>
- Letter from: 15.4.1933, Brüssel
- Letter from: 25.4.1933, Comologno (Switzerland)
- Compagnie des Messageries Maritimes <Paris>
- Letter from: 20.1.1936, Zurich (Switzerland)
- Compagnie Madeleine Renaud-Jean-Louis Barrault <Paris>
- Letter from: 17.12.1952, New York (N.Y.)
- Conditorei und Caféhaus Hanselmann <St. Moritz>
- Letter from: 30.12.1925, St. Moritz
- Confiserie Erich Hamann <Berlin>
- Letter from: 16.1.1925, Charlottenburg
- Letter from: 13.2.1925, Fürstenberg (Germany)
- Letter from: Ostersamstag 1938 [=16.4.1938], London (England)
- Conservatorium <Jerusalem>
- Letter from: 29.5.1935, Jerusalem
- Letter from: 26.6.1935, Jerusalem
- Cook Reisebüro
- Letter from: 8.1.1929, Menton / Alpes-Maritimes (France)
- Letter from: 9.10.1933, London (England)
- Letter from: 17.12.1934, Egypt [auf dem Nil]
- Cook Reisebüro <Cannes>
- Letter from: 15.2.1933, Antibes (France)
- Cornell Architecture School
- Letter from: 7.12.1941, New York (N.Y.)
- Letter from: 22.8.1950, New York
- Corviglia Hütte <St. Moritz>
- Letter from: 17.6.1946, San Francisco
- Cyclotron <Berkeley>
- Letter from: 30.4.1942, San Francisco
