Arabidopsis trichomes are single-celled hairs that originate from epidermal cells and are distributed regularly on most aerial body parts. During the last decade, trichome formation in Arabidopsis has been established as a genetic and molecular model system to study various general developmental and cellular mechanisms. This review summarizes progress in the investigation of several aspects of trichome development: the spatial regulation of cell fate determination, the regulation of cell differentiation in response to exogenous signals and plant hormones, and the regulation of endoreplication, cell growth, and cell morphogenesis.