 We begin with the logical problem of truthlikeness: the problem of giving an adequate account of the concept and determining its logical properties. In §1 we lay at the logical problem and various possible solutions to it. In §1.1 we examine the basic assumptions which generate the logical problem, which in part explains why the problem emerged when it did. Attempted solutions to the problem quickly proliferated, but they can be gathered together under three broad lines of attack. The first two, the content approach (§1.2) and the consequence approach (§1.3), were both initiated by Popper in his ground-breaking work; although Popper’s specific proposals did not capture the intuitive concept (and were technically inadequate), the content and consequence approaches are still being actively developed and refined. The third, the likeness (or similarity) approach, takes the likeness in truthlikeness seriously; the main results and problems facing the likeness approach are outlined in §1.4.