Compared to phonology, morphology, or syntax, lexical and propositional semantics of heritage languages remain understudied. Interference from lexical items of the dominant language is a notable factor, but such interference is less pronounced than in L2 speakers. Heritage often create novel expressions by tapping into structures available from both of their languages and combining them in innovative ways. One of the most prominent characteristics of heritage lexicon is extreme reliance on fully compositional structures. Heritage speakers seem to have knowledge of non-compositional formations in their dominant language, but they seem to shun non-compositionality in their weaker language. Semantically opaque expressions tend to be avoided in favor of the semantically transparent ones. Turning to propositional semantics, few of its aspects have been explored in heritage language. The existing evidence suggests a strong interaction between the bilingual’s two languages in this domain. In particular, in scope calculations, it appears that the two systems push at each other. In such an interaction, the simpler system wins out, reducing complexity in one of the two languages in the dyad. Heritage speakers’ knowledge of pragmatics remains unchartered territory, and making progress in this area is particularly difficult since researchers’ understanding of pragmatic competence varies tremendously.