In these essays, Andrew Cunningham is concerned with issues of identity - what was the identity of topics, disciplines, arguments, diseases in the past, and whether they are identical with (more usually, how they are not identical with) topics, disciplines, arguments or diseases in the present. Historians usually tend to assume such continuous identities of present attitudes and activities with past ones, and rarely question them; the contention here is that this gives us a false image of the very things in the past that we went to look for.