The grass family (Poaceae) is unusually well known taxonomically, with over 10,000 described species. These are characterized and classified according to a variety of morphological characters, particular those of the inflorescence and the spikelet but also a wealth of micromorphological and moleculary characters. Much data on the family is accessible electronically. Available phylogenies have identified 12 major lineages that are classified as subfamilies; within these subfamilies, especially for subfamily Panicoideae, the phylogeny is becoming increasingly clear. Developmental studies focus on the activity and fate of meristems throughout the plant, and illustrate how adult morphology arises. Analyses of quantitative trait loci (QTL) verify that some taxonomic characters are controlled by distinct genes, thus supporting their use in taxonomy. Studies of gene expression identify several genes, including LEAFY HULL STERILE1, RAMOSA1, and TEOSINTE BRANCHED1 that may have contributed to diversification of the grasses.