  This volume contains the proceedings of EXPRESS/SOS 2023: the Combined 30th
International Workshop on Expressiveness in Concurrency and the 20th Workshop
on Structural Operational Semantics, which was held in Antwerp, Belgium, as an
affiliated workshop of CONCUR 2023, the 34rd International Conference on
Concurrency Theory. The EXPRESS/SOS workshop series aims at bringing together
researchers interested in the formal semantics of systems and programming
concepts, and in the expressiveness of computational models.
