The dominant effect of transcription factors in imparting expanded potency is best exemplified by the reprogramming of fibroblasts to pluripotent cells using retrovirus-mediated transduction of defined transcription factors. In the murine system, Oct4, Sox2, c-Myc and Klf4 are sufficient to convert fibroblasts to induced pluripotent stem (iPS) cells that have many characteristics of embryonic stem (ES) cells. Here we show that the orphan nuclear receptor Esrrb functions in conjunction with Oct4 and Sox2 to mediate reprogramming of mouse embryonic fibroblasts (MEFs) to iPS cells. Esrrb-reprogrammed cells share similar expression and epigenetic signatures as ES cells. These cells are also pluripotent and can differentiate in vitro and in vivo into the three major embryonic cell lineages. Furthermore, these cells contribute to mouse chimaeras and are germline transmissible. In ES cells, Esrrb targets many genes involved in self-renewal and pluripotency. This suggests that Esrrb may mediate reprogramming through the upregulation of ES-cell-specific genes. Our findings also indicate that it is possible to reprogram MEFs without exogenous Klf transcription factors and link a nuclear receptor to somatic cell reprogramming.