This special volume of Information and Computation aims at documenting state-of-the-art research, new developments, and directions for future investigation in the field of structural operational semantics (SOS). It includes papers about the SOS of concurrent processes, addressing ordered SOS, simulation up-to, mobility, name-passing, and congruence formats. It also contains papers about the SOS of programming languages, focussing on bialgebraic semantics, co-inductive and bi-inductive forms of

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... ig-step SOS, the relationship to rewriting logic semantics, and the use of logical relations. Since its introduction by Robin Milner [1] and Gordon Plotkin [2] around 1980, SOS has become one of the main semantic description frameworks. It has been used to describe the static and dynamic semantics of numerous programming and concurrent process languages, and some non-executable specification languages. Its most characteristic feature is the use of axioms and inference rules to define transition relations, which are usually structural in the sense that transitions for compound phrases are inferred from transitions for their sub-phrases. SOS has considerable intuitive appeal and flexibility, and is based on simple and familiar mathematical foundations. At the same time, it is remarkably powerful. For instance, when a concurrent process language is defined by an SOS whose rules are in a restricted format, various useful properties of the language, such as compositionality of its operators with respect to a given semantic equivalence, are ensured. This volume is an outgrowth of the series of SOS workshops, which started in 2004, and contains full versions of several papers presented at SOS