W.D. Hamilton, one of the most influential evolutionary biologists of the twentieth century, was fascinated and puzzled by social wasps. Towards the end of his academic career, Hamilton openly admitted that: “... it was to social life that wasps were providing my touchstone puzzles” (Hamilton 1996, vi). This article deals with Hamilton’s attempts to understand social life in wasps mostly in the 1960s. First, it provides an overview of the reasons why Hamilton thought social wasps constituted a puzzle. Second, it shows how Hamilton tried to deal with this puzzle, by performing experiments, conducting observations and eventually modifying his theory by including factors, most notably inbreeding, that he had not clearly considered in its first formulation.