Richard Sylvan contributed widely to logic throughout his career. Apart from a series of papers on modal logic(several written with Hugh Montgomery) in the late 1960's early 1970's, most of his work was on non-classical logics, especially their semantics. Early work included a rehabilitation of Alexius Meinong's theory of objects, starting with papers in the 1960's and culminating in the massive Exploring Meinong's Jungle and Beyond (1980). Other work started in the 1960 was on significance and context logic, done mainly in collaboration with Leonard Goddard and culminating in their Logic of Significance and Context (only the first volume of which was ever completed). Probably his most important contribution to logic was the development, in collaboration with Robert Meyer and Val Routley, of the first semantics for relevant logic. Starting in the early 1970's, relevant logic remained a major interest until his death, resulting in many notable publications: including the series of joint papers with Meyer on "Semantics of Entailment"; Relevant Logics and their Rivals (vol. 1: 1983), written jointly with Meyer, Val Routley (now writing under the name Plumwood) and Ross Brady (the second volume was completed by Brady after Sylvan's death); a collection of edited papers, Directions in Relevant Logic (1989); and the posthumously published Sociative Logics and their Applications (2000), edited by Dominic Hyde and Graham Priest. Sylvan's interest in relevant logic expanded into work on paraconsistent logic more generally and into dialethic logic, often in collaboration with Graham Priest (e.g. their jointly edited Paraconsistent Logic, 1989). There were many other interests as well: universal semantics and the ultralogic program in the 1970's and 1980's; work on vagueness in collaboration with Hyde; and work on problems in artificial intelligence.