This invention relates to the culture of pluripotent cells in a fully humanised chemically defined medium. Cells may be cultured over a prolonged period of time without losing their pluripotent status or may be controllably induced to differentiate into progenitor cells of the three primary germ layers by the addition of differentiation factors, for example differentiation factors which modulate one or more of the Activin/Nodal, FGF, Wnt or BMP signalling pathways.