The fruit is a highly specialized plant organ that occurs in diverse forms among the angiosperms. Fruits of Arabidopsis thaliana, which are typical of the > 3000 species of Brassicaceae, develop from a gynoecium that consists of two fused carpels. The mature gynoecium of Arabidopsis is composed of an apical stigma, a short style, and a basal ovary that contains the developing ovules. After the ovules are fertilized, the fruit elongates and differentiates a number of distinct cell types, allowing for the successful maturation and the eventual dispersal of the seeds. Although the processes involved in carpel and fruit morphogenesis are not well understood, recent studies have identified a large number of mutants that display abnormal gynoecium and fruit development. The detailed phenotypic description of these mutants together with recent cloning of many of these genes has begun to shed light on this interesting and complex developmental process. Here we review the growing collection of Arabidopsis genes known to control the initiation and development of the gynoecium and resulting fruit.