The genus Banisteriopsis is one of the largest and most widespread genera in the Malpighiaceae. The genus has presented considerable difficulty to botanists interested in the correct identification of plants in this genus because many of the species are very variable, have considerable synonymy, and even the name of the genus has presented nomenclatural problems. The last monographic revision of the genus by Franz Niedenzu (1928) recognized 74 species. Since that time, much additional material of Banisteriopsis has accumulated, and in the present revision I recognize 92 species of which 34 are new. Many of the widespread and variable species still present problems, but I hope that I have been able to identify these problem areas for further study. Soon the name of this largegroup of neotropical plants will finally be stabilized.