Marine bryozoans are a rich source of bioactive metabolites, some of which have been evaluated for their pharmaceutical potential. Though the ecological roles of these bryozoan metabolites have not been extensively explored, some of them are known to deter predation, fouling, and substrate settlement by other sessile invertebrates. Not surprisingly, these bryozoan metabolites influence trophic interactions. The ecological studies highlighted in this chapter highlight the complexities of bryozoan chemical ecology: bryozoans regulate their bioactive metabolites spatiotemporally and employ metabolites that are derived from their own biosynthesis or from their symbiotic partners.