Hancock is recognised as one of the founders of the field of pidgin and creole linguistics. He has also done extensive research on the English-based creole languages spoken in West Africa and the West Indies. He is known especially for his views on the historical development of these languages. He maintains that all the English-based pidgins and creoles spoken in the Atlantic basin region, both in West Africa and in the Caribbean, belong to a single language family, which he calls the "English-based Atlantic Creoles." He argues that all of them can be traced back to what he calls Guinea Coast Creole English, which arose along the West African Coast in the 17th and 18th centuries, as a language of commerce in the Atlantic slave trade. He says that Guinea Coast Creole English was spoken in coastal slave trading bases such as James Island, Bunce Island, and Elmina Castle, where the offspring of British slave traders and their African wives used it as their native language.