The main text of Popper's Logik der Forschung (1935) consists of seven chapters outlining the main features of his falsificationist philosophy of science, followed by two involving probability theory and quantum mechanics, and finally one on corroboration, which is the main concern here. (I shall cite his English translation of the book (Popper 1959), noting its newer material when appropriate.) The chapter begins with a section on non-verifiability of theories, which would have been better placed in chapter 6 on testability, and then two sections on the probability of events and of hypotheses and on probability logic, which belong rather in chapter 8. Only then come four short sections on corroboration, the property of a theory that it passes its tests. The chapter is placed last because of a link between corroboration and probability; he even claimed that there was no difference between the two in that both are appraisals (1959, 265). In a later appendix *ix, and in more detail in other work (1982a, 240-255), he offered quantitative measures of corroboration involving probabilities, but at the end of the latter text he almost dismissed the enterprise; and in similar vein, I shall not consider it further, since the measures depend upon the tests which happen to have been carried out and so are not very significant. Otherwise, he did not discuss corroboration very much in his writings, and it is not well handled by commentators;1 but this rather low status contrasts markedly with the actual practice of science, where scientists and engineers regularly work with (seemingly) highly corroborated theories, even to the extent that "reliability science' is a subject in its own right.