The carpel is the female reproductive organ that encloses the ovules in the flowering plants or angiosperms. The origin of the carpel and its subsequent morphological modifications were probably of vital importance to the evolution of the angiosperms, and the carpel is also very important as the precursor organ to the fruit. Here we describe the general attributes of the angiosperm carpel and several hypotheses for its evolutionary origin. As carpels share many developmental processes with leaves, we describe these processes in the leaf, and then detail the regulation of carpel and fruit development in the model angiosperm Arabidopsis thaliana. We also describe the relationship between carpel formation and the arrest of organ proliferation which occurs at the centre of the Arabidopsis floral meristem. We then provide a brief overview of carpel development in angiosperms occupying important phylogenetic positions, including ANA grade angiosperms, monocots, basal eudicots and core eudicots, focussing on the probable ancestral state of the carpel in each case, and on the available molecular and genetic data. We end with a brief discussion of future research directions relating to carpel and fruit development.