In 1978, Howard Scott Gentry published his second monograph on the genus Agave focusing on the plants of the peninsula of Baja California, México, and the related species in the group Deserticolae in the US and Sonora. We revisit Gentry's work with an emphasis on revising the genus and its taxonomic arrangement and including several recently described species from this Mexican peninsula known for its high plant endemism. A total of 23 Agave taxa occur on the peninsula, 22 of which are endemic. We change Gentry's treatment of four groups into six sections formally defined to better segregate species based on shared inflorescence characteristics. We eliminate one variety, revert one variety to species status, change two species to subspecies or varieties, and reduce one subspecies to a variety. We present high spatial resolution maps of the distribution of these species as well and correct some of the previous identifications of herbarium specimens. Extensive field work suggests that taxonomic problems remain in the Agave sobria complex of the Sierra de la Giganta, where as many as three additional taxa could be described from the array of variation we observed. As well, the distributional overlap of Agave avellanidens and Agave shawii ssp. goldmaniana remains problematic owing to similar vegetative characteristics but greatly differing inflorescences.