Vegetative and reproductive morphology and their variation within Aneilema, one of the largest genera of Commelinaceae, are described in detail. The taxonomic usefulness of the various characters is considered, and floral attributes are found to be particularly important. Within the genus, great diversity is found in habit, pedicel curvature, petal color, stamen curvature, floral hair types and distribution, and seed shape and testa patterns. Anatomy, cytology, phytochemistry, and reproductive biology of Aneilema are treated briefly. Aneilema is divided into seven sections, with sections Rendlei, Somaliensia, Brevibarbata, and Pedunculosa described as new. Keys to the sections and to all 62 species recognized are provided. The 22 species comprising sections Rendlei, Somaliensia, and Lamprodithyros are treated in detail, with nine new species and five new subspecies described. One naturally occurring hybrid is also newly recognized. Two species originally described in Aneilema but of uncertain generic position, A. calandrinoides and A. brasiliense, are discussed in detail. A list of all specific names that have ever been included in Aneilema and their current status (including new combinations and new synonymy, when appropriate) is appended.