Saul Winstein (October 8, 1912 – November 23, 1969) was a Jewish Canadian chemist who discovered the Winstein reaction. He argued a non-classical cation was needed to explain the stability of the norbornyl cation. This fueled a debate with Herbert C. Brown over the existence of σ-delocalized carbocations. Winstein also first proposed the concept of an intimate ion pair. He was co-author of the Grunwald–Winstein equation, concerning solvolysis rates.
Richard F. Heck, who earlier in his career had undertaken postgraduate studies with Winstein, won the 2010 Nobel Prize in Chemistry.