  This volume contains the proceedings of the Combined 23nd International
Workshop on Expressiveness in Concurrency and the 13th Workshop on Structural
Operational Semantics (EXPRESS/SOS 2016) which was held on 22 August 2016 in
Qu\'ebec City, Canada, as an affiliated workshop of CONCUR 2016, the 27th
International Conference on Concurrency Theory. The EXPRESS workshops aim at
bringing together researchers interested in the expressiveness of various
formal systems and semantic notions, particularly in the field of concurrency.
Their focus has traditionally been on the comparison between programming
concepts (such as concurrent, functional, imperative, logic and object-oriented
programming) and between mathematical models of computation (such as process
algebras, Petri nets, event structures, modal logics, and rewrite systems) on
the basis of their relative expressive power. The EXPRESS workshop series has
run successfully since 1994 and over the years this focus has become broadly
construed. The SOS workshops aim at being a forum for researchers, students and
practitioners interested in new developments, and directions for future
investigation, in the field of structural operational semantics. One of the
specific goals of the SOS workshop series is to establish synergies between the
concurrency and programming language communities working on the theory and
practice of SOS. Since 2012, the EXPRESS and SOS communities have organized an
annual combined EXPRESS/SOS workshop on the expressiveness of mathematical
models of computation and the formal semantics of systems and programming
concepts.
