Allyl sulfides have gained traction in recent years as promoters for olefin metathesis. The high reactivity of allyl sulfides in olefin metathesis is remarkable, given that many sulfur-containing substrates are incompatible with ruthenium-based olefin metathesis catalysts. In stark contrast, allyl sulfides actually enhance the rate of metathesis in comparison with other alkenes, when matched with a suitable catalyst. This review examines how the high reactivity of allyl sulfides in olefin metathesis has been harnessed in diverse areas of synthesis. In the cases examined, allyl sulfides have been explicitly incorporated into substrates to promote olefin metathesis. Recent insights into catalyst considerations, applications in chemical and biochemical synthesis, and future opportunities are discussed.