The nature of semantic roles and grammatical relations are explored from the perspective of Role and Reference Grammar (RRG). It is proposed that unraveling the relational aspects of grammar involves the recognition that semantic roles fall into two types, thematic relations and macroroles, and that grammatical relations are not universal and are not constituted in the same way in every language in which they exist. The concepts of thematic relations, semantic macroroles, and grammatical relations are explained, and evidence of cross-linguistic variation in grammatical relations is presented from a variety of languages including Acehnese, Zapotec, Walpiri, English, and Dyirbal. Implications for language acquisition and the analysis of child language are also discussed. (MSE)