The deep sea is increasingly recognized as a fertile area for offshore industrialization. If existing activities in the deep sea continue or are expanded and new deep-ocean industries are developed, there is need to consider what is required to minimize repair resulting in damages to the deep-sea environment. This article in the journal Marine Policy develops the discourse on deep-sea restoration and offers guidance on planning and implementing ecological restoration projects for deep-sea ecosystems that are already, or are at threat of becoming degraded, damaged or destroyed. Two deep-sea restoration case studies in Scotland and Papua New Guinea are described and are contrasted with on-going salt marsh restoration in the San Francisco Bay.