1. Herbert Feigl Papers, University Archives, University of Minnesota, Twin Cities Campus, Minneapolis.
2. Moritz Schlick Papers. Wiener Kreis Archiv, Noord-Hollands Archief, Haarlem.
3. P. W. Bridgman Papers. Harvard University Archives, Harvard University.
4. Rudolf Carnap Papers. Archives of Scientific Philosophy. Hillman Library, University of Pittsburgh.
5. Sidney Hook Papers, Hoover Institution Library and Archives, Stanford University