The free movement of goods, services, capital and labour within Europe is not based on European Union (EU) membership. Single market access is based on membership the EEA, of which every EU state is an automatic member. Every member of EFTA (European Free Trade Association) is also entitled to join, but are not compelled to do so. Norway has exercised that right, whereas Switzerland considered doing so but the proposition was voted down at a referendum.
Source : Knight Frank