Summary Brassinosteroids (BRs) are steroid hormones ubiquitously found in plants but first purified from Brassica. BRs contribute to growth, vascular differentiation, reproductive development, and stress responses. In the 1990s BR biosynthesis and response mutants were identified, allowing the complete pathway from synthesis to response to be assembled. BRs are remarkable in the diversity of their actions, and have potential applications ranging from improving plant stress tolerances to increasing grain yields.