A series of seminal experiments demonstrated that ectopic expression of few critical genes drives conversion of a somatic to a pluripotent cell state. Induced pluripotent cells (iPS) were first generated from murine fibroblasts by transfection with retroviral vectors expressing four transcription factors: Oct4, Sox2, Klf4 and cMyc. Subsequent experiments applied this technology to other somatic cell types and so far iPS cells have been generated in rodent, human and non-human primate species. Particular somatic cell types seem to be better candidates for cellular reprogramming and in those iPS can be generated by an even smaller number of transcription factors. The efficiency of conversion and maintenance of a pluripotent state can be supported by small molecules, and specific pharmacological inhibitors. This technology is a milestone for basic understanding of cell potency, cell fate and pathogenesis, as well as for development of cell therapies in humans and potential applications in animal breeding. In large mammalian species were no genuine embryonic stem cells could be developed within the last two decades, the iPS technology promises an alternative approach for pluripotent cells.