This pioneering book investigates how biographical evidence has been variously used, misused, or not used at all, by clinicians entirely reliant on biographical evidence for the influential posthumous diagnoses they have produced of Winston Churchill as a manic-depressive. Attention is paid, also, to the distinct question of Churchill and “nerves,” otherwise known as neurasthenia. This question has a place alongside the manic-depression issue because, by ensuring there is a marked contrast between two lines of biographical inquiry, it facilitates a significant move in the direction of a more rounded, a more securely founded, understanding of how Churchill functioned psychologically, and how he did not. That goal of a more rounded understanding is important, and the contribution Diagnosing Churchill makes towards its achievement is worthwhile, because accuracy in the depiction of key elements in the functioning of a major historical figure, one of the heroes of Western democratic civilization, is enjoined by a principle Churchill expressed thus: “the meanest historian owes something to the truth.”