 Of substantially greater note for the foundations of quantum theory are six papers by von Neumann (three jointly published with Murray) on rings of operators, which are reprinted in von Neumann (1961–1963, Vol. III, Nos 2–7). The first two, “On Rings of Operators” and a sequel “On Rings of Operators II”, were published in 1936 and 1937, and they were seminal to the development of the other four. The third, “On Rings of Operators: Reduction Theory”, was written during 1937–1938 but not published until 1949. The fourth, “On Infinite Direct Products”, was published in 1938. The remaining two, “On Rings of Operators III” and “On Rings of Operators IV” were published in 1941 and 1943, respectively. This massive work on rings of operators was very influential and continues to have an impact in pure mathematics, mathematical physics, and the foundations of physics. Rings of operators are now referred to as “von Neumann algebras” following Dixmier (1981), who first referred to them by this name (stating that he did so following a suggestion made to him by Dieudonné) in the introduction to his 1957 treatise on operator algebras (Dixmier 1981).