Annual species of Geranium from North America north of Mexico are revised. Eleven species are accepted, of which six belong in subg. Geranium and five belong in subg. Robertium. Geranium bicknelli, G. carolinianum, and G. texanum are the only native species, whereas G. aequale, G. columbinum, G. dissectum, G. lucidum, G. molle, G. pusillum, G. robertianum, and G. rotundifolium were introduced from the Old World. Geranium sphaerospermum, sometimes accepted in current literature, is considered to be a synonym of G. carolinianum. Nomenclature for all species is reviewed, and eight lectotypes are designated. Descriptions, key, distribution maps, and illustrations are included.