Wild Brassica plants release seeds by a pod shattering mechanism; in related crop plants, such as oil‐seed rape, this can result in substantial loss of seed, and hence loss of revenue, and also in the distribution of seeds which can contaminate future crops and the environment. To identify strategies which may be used to reduce shatter, either by conventional breeding programmes or by genetic engineering, we have examined fruit development in oil‐seed rape (Brassica napus), and in the related B. juncea and Arabidopsis, using a combination of cytological, cytochemical and molecular techniques. We report here on the patterns of cellular differentiation and tissue development during fruit maturation, and suggest how this results in the shattering phenotype.