 The Aufbau was largely drafted before Carnap joined the Vienna Circle. Once there and under some influence from Neurath, Carnap campaigned more insistently for physicalism and for the unity of science. They seemed often to be two sides of the same coin. From 1933 onward there was a succession of monograph series with ‘Unified Science’ in the title. Until his death in 1945, Neurath was in each case the main editor and Carnap either the associate editor or one of the associate editors. The International Encyclopedia of Unified Science, begun in 1938 is undoubtedly the most famous of these. Carnap’s own essay on this topic “Logical Foundations of the Unity of Science” (1938) was printed as part of the very first number in the encyclopedia.