Predominantly marine (no fresh water forms reported from Bermuda), on stable substrates. Calcarea are most common in very shallow water; Demospongea (95% of all recent species) occur in all depths and climate zones but, except for small, crustose and endolithic forms, avoid high energy environments. Substrates include rock (especially in caves), dead coral, subtidal mangrove roots, sea grass rhizomes, algae, other sponges, shells of molluscs and crabs, and artificial structures (bouys, pilings). Soft bottoms in calm water are colonized by initial settlement on rubble fragments.

Life-span ranges from a few months to about 10 years; some very large specimens (0.8 to 2.5 meters in diameter) of Demospongea observed in deep reef zones, outside the range of wave-action, are estimated to be between 50 and 100 years old.

Many tropical and subtropical shallow water species harbour symbiotic bacteria and unicellular algae.