What does it mean to say that a scientific theory is unified? Prominent attempts by John Watkins, Philip Kitcher, and Margaret Morrison to answer this question face serious difficulties, and many analysts of science remain pessimistic about the possibility of ever rendering precise or explaining what theoretical unity consists in. This paper gives grounds for optimism, offering a novel account of the concept of unification. This account is tested against a detailed study of the standard model in contemporary high-energy physics, a theory for which a high degree of unity has repeatedly been claimed.