Rice (Oryza sativa) grain shape is a key determinant of grain yield and market values. Facilitated by advancements in genomics and various molecular markers, more than 400 quantitative trait loci (QTLs) associated with rice grain traits have been identified. In this review, we examine the genetic bases of rice grain shape, focusing on the protein products of 13 genes that have been cloned and the chromosome locations of 15 QTLs that have been fine mapped. Although more genes affecting grain traits are likely to be cloned in the near future, characterizing their functions at the biochemical level and applying these molecular data to rice breeding programs will be a more challenging task.