Abstract. This study investigates the role of mood markers in the semantic composition of complex sentence constructions, on the basis of a sample of Australian languages. The question of mood marking in complex sentences is theoretically significant because it involves a clause-internal category that plays a crucial role in the semantics of a construction above the level of the individual clause. Previous work on mood in complex sentences has shown that presence of mood marking in one of the component clauses tends to correlate with a feature of non-actualization on the level of the complex sentence. In this paper, I argue that this semantic generalization actually obscures a number of constructionally relevant distinctions, because there are two additional factors that determine the precise role of the mood marker in the complex sentence: (1) the presence or absence of specifically relational markers like conjunctions and (2) the semantically schematic or specific nature ofthese markers. In constructions without relational markers, mood markers do not strictly speaking encode the complex sentence relation, but pragmatically trigger it. In constructions with relational markers, on the other hand, mood markers and relational markers jointly encode the complex sentence relation, but their relative contribution depends on a principle of functional trade-off.Introduction. In the analysis of complex sentence constructions, we can make a basic distinction between two broad categories of markers that contribute to the semantic specification of the complex sentence relation. On the one hand, there are markers like conjunctions or complementizers, which can be called relational markers: these are generally found only in complex sentences and thus serve as specialized markers for labeling complex sentence relations like causal, conditional or temporal relations. On the other hand, there are also intra-clausal markers like tense, aspect and mood markers: by specifying component clauses for particular temporal or modal features, these markers can equally contribute to the semantics of complex sentence relations, but unlike conjunctions they are not specialized in complex sentences. Intra-clausal markers are part of the internal structure of the simple clauses that make