In this Introduction there are three questions considered: first, when did the eighteenth century in British philosophy begin and end? Secondly, is there a reason to talk in terms of British philosophy in this period, as different and distinct from English, Scottish, Welsh, and possibly also Irish and American philosophy? Thirdly, how should philosophy be defined in an eighteenth-century British context? Then the unit endeavours to explain how British philosophy evolved since the 18th century.