This article provides an overview of process tracing, concentrating on the dimensions of this method that are relevant to Bayesian logic. It also briefly outlines the logic of Bayesian inference, emphasizing parallels with the logic of process tracing. The article shows these points with examples from the historical explanation of political events, including the 1898 Fashoda crisis, the end of the First World War, and the end of the Cold War. It concludes that Bayesianism helps in understanding the strengths of case-study methods, including their potential to develop and test explanations even with limited evidence drawn from one or a few cases, and their limits, including the provisional nature of historical explanations and the challenges of generalizing from small numbers of cases. The ‘Degrees of Freedom’ problem is inapplicable to process tracing, even though the more fundamental problem of underdetermination remains.