This article deals with the representation of complement sentences in a speaker's mental grammar, and the contribution of complement-taking predicates and complement clause types to the overall meaning of the complement sentence. Either complement-taking predicates alone, or both complement-taking predicates and complement clause types have been argued to have meanings that contribute to the overall meaning of the complement sentence. The article examines the distribution of various complement clause types in Ancient Greek, and argues that this distribution is best accounted for in a constructionist model. In this model, individual combinations of complement-taking predicates and complement clause types are constructions, that is, grammatical entities independent of the words in the sentence, with both formal structure and semantic and pragmatic content. The latter is associated with the combination “complement-taking predicate + complement clause type” as a whole, rather than being part of the mental representation of either the complement-taking predicate or the complement-clause type as such. Form-meaning relations in complement constructions are also discussed.