Technical Abstract: Until recently, little has been known about the molecular mechanisms that establish and maintain stem cell populations in the apical meristems of plants. However, genetic and molecular evidence now convincingly demonstrates that maintenance of the meristematic state throughout development is mediated by a complex network of positive and negative regulatory interactions. Much of the data has come from studies using the model plant Arabidopsis thaliana, a member of the mustard family and a relative of broccoli and cauliflower, on which this article will focus.