Human embryonic stem cells (ES) hold promise because of their ability to give rise to any human cell type. To realize this promise, methods are needed to control human ES cell differentiation and to generate large populations of undifferentiated cells. In organisms, stem cell proliferation and differentiation is controlled by the local environment, commonly referred to as the stem cell niche. In their niches, cells receive signals from soluble compounds (e.g., growth factors), other cells, and a collection of proteins and polysaccharides referred to as the extracellular matrix We are combining surface science and organic synthesis to create synthetic niches. We have developed a new strategy to synthesize surface arrays, which can be used to guide the design of these synthetic niches. This strategy provides a powerful new method to control human ES cell decisions.