The Meaning of Semantics

I will present three main themes in current research in semantics: (a) models of programming languages, (b) concurrency and (c) approximation. The first theme covers denotational semantics and operational semantics and the search for tight connections between them. This led to the full abstraction problem and ultimately to game semantics. The second theme began with the attempt to understand processes and the realization that there were brand new issues to deal with. In particular it was hard to even find compositional models at first. Finally, domain theory originally invented to provide set-theoretic models of the lambda calculus, turned into a general theory of approximation and has had an impact on the theory of probabilistic processes.