A discussionis presented of environmental controls that affect the preservation of archaeological artefacts in the marine environment. Physical, biological and chemical degradation processes are discussed although it is appreciated that these processes operate in conjunction and often in a site-specific manner. Two Irish case studies are presented of environmental controls on shipwreck preservation: The Kish Bank, Outer Dublin Bay and La Surveillante, Bantry Bay. These illustrate contrasting environmental factors affecting shipwreck preservation.