Direct reprogramming of somatic cells into induced pluripotent stem (iPS) cells is a valuable method to produce patient-specific stem cells of any lineage without the use of embryonic materials. Various new strategies have been developed to improve the reprogramming technologies since the first report of iPS cells generation from murine fibroblasts using retroviral transduction of a defined set of transcription factors. Methods of factor reprogramming fall into two broad categories: chemical and transgene reprogramming.