Marine-derived enzymes have recently gained attention particularly for industrial applications. Cellulose-degrading enzymes are among leading biocatalysts with potential utility in biorefineries. This review presents an account of the cellulase production by marine sources from microorganisms including bacteria, yeasts, and molds to marine invertebrates such as protist, rotifer, mollusks, arthropods, and echinoderms. Cellulose-degrading ability of marine invertebrates is attributed to the production of endogenous cellulases and activities by the symbionts. Specialized environments in marine including estuaries and mangroves are rich in lignocellulosic biomass and hence provide a feeding ground for cellulose digesters. Since cellulosic biomass is considered chemical and energy feedstock, therefore, cellulases with the ability to work under extreme environment are much needed to fulfill the demand of modern biotechnological industries. The review also discusses physicochemical parameters of marine-derived cellulases.