Douglas Ross is renowned for his seminal contributions to the development and exploitation of gauge theories, both within and beyond the Standard Model of particle physics. His work has led to the understanding of the renormalisation structure of spontaneously broken theories and to the theoretical properties of the perturbation series in non-Abelian theories. He performed a number of the early perturbative calculations which helped establish quantum chromodynamics as the theory of the strong nuclear force. Among his contributions to physics beyond the Standard Model was the demonstration that the non-observation of proton decay excluded the simplest Grand Unified Theory.