Additive transgenesis by pronuclear injection of the mouse zygote has been in use for more than 20 yr and gene targeting in mouse embryonic stem cells for almost as long. Together, these techniques have revolutionized animal biology by helping to unravel much of what we now know about gene function. Both additive transgenics and targeting can also be performed in livestock species but the impact has not yet been substantial. In part, this has been the result of the inefficiency of the techniques but?at least in agriculture?also to a lack of obvious practicality. This review assesses the extent to which this situation is changing, with particular reference to applications in biopharming, xenotransplantation, and large animal models