 Reichenbach’s views on underdetermination in physics were developed extensively by Adolf Grunbaum, but as a metaphysical rather than epistemological thesis. The issue of the conventionality of simultaneity relations has attracted a large philosophical literature. Reichenbach’s Principle of the Common Cause has attracted extensive philosophical comment, much of it devoted to purported counterexamples to a strict universal claim that Reichenbach explicitly denied. Without reference to Reichenbach, the principle was restated in the 1950s by Herbert Simon (1954) as a claim about the explanation of “spurious” correlations. Under the name “Markov condition,” in the early 1980s Reichenbach’s principle was generalized by several statisticians, most notably Terry Speed (Kiiveri &amp; Speed, 1982), and today plays an essential role in representation and search for causal relations. We do not know whether Simon, who had been Carnap’s student at the University of Chicago, knew of Reichenbach’s ideas; the statisticians very likely did not. Perhaps not coincidentally, the senior author of this entry, who helped to develop the directed graphical representation into search and prediction procedures for causal hypotheses, studied with two of Reichenbach’s doctoral students, Schuster and Salmon. As noted above, Reichenbach anticipated formulations of probabilistic causal relevance advanced by Patrick Suppes in A Probabilistic Theory of Causality (1970), and the use of “marks” can be found in a somewhat different guise in Salmon (1984) and Dowe’s (2000) work on causality. 