Marine hard-substrate communities are important ecological and evolutionary resources for paleontologists and neontologists, yet their study is handicapped by numerous terms that are used inconsistently. A rationalized nomenclature system is proposed for plants and animals that encrust or bore natural marine hard substrates. The terms describe the identity of the colonizing organism, the nature of the substrate, and the location of the colonist (on the surface or within the substrate). These terms follow simple principles, making them easy to construct and interpret. A new collective term also is introduced: a sclerobiont is any organism (animal or plant) fouling any kind of hard substrate.