This paper describes the materials in the Russell Archives relevant to Russell's work on logic and the foundations of mathematics, and suggests the kinds of information that may and may not be drawn about the historical development of his ideas. By way of illustration, a couple of episodes are described. The first concerns a logical system closely related to his theory of denoting, which preceeds the system used in Principia mathematics, while the second describes a delay in publishing the second (...) volume of that work due to the discovery by Whitehead of a conceptual error. (shrink)