Semantic role is the actual role a participant plays in some real or imagined situation, apart from the linguistic encoding of those situations. Semantic roles, also known as thematic roles, are one of the oldest classes of constructs in linguistic theory. Semantic roles are used to indicate the role played by each entity in a sentence and are ranging from very specific to very general. Also, semantic roles are useful in natural language processing. They have proved attractive because they provide a way of representing commonalities across different uses of the same predicate or across uses of distinct but semantically related predicates that may be obscured because arguments with certain semantic roles may have various syntactic realisations. Thus they provide a level of abstraction for the statement of generalisations concerning a variety of linguistic phenomena. In particular, argument realisation generalisations are often stated over a thematic hierarchy, a ranking of semantic roles. However, semantic roles have not lived up to their initial promise. It has proved impossible to find a small set of roles that can be applied across all verbs in a language, let alone across languages. Advances in Research on Semantic Roles provide more sustained discussion of the notion of semantic role. It often traces the development of the notion, as well as its place within current linguistic theory. In addition, it introduces several approaches to semantic role inventories, highlighting the similarities and differences among them, and discusses the limitations both of particular approaches and of semantic role approaches in general. Semantic roles continue to be useful in stating linguistic generalisations, and so descriptive, if not theoretical, uses of semantic role labels persist across subfields, including language acquisition, psycholinguistics, and neurolinguistics.