Biotechnology policy in the United States promotes the commercial development of genetically modified crops, yet adopts a precautionary approach when it comes to stem cells and cloning. In this article, the evolution of this bifurcated policy domain is traced. A detailed analysis of congressional hearings shows how distinctions between the products of biotechnology came to be reflected in the character of committees holding hearings, the attention to risks and benefits, and the pattern of interest-group activity in different biotechnology applications. It is argued that many of the differences that separate the United States and Europe in biotechnology reflect the way institutions reinforce past policy choices.