The aim of this paper is to explain the development of the social economy in the United Kingdom (UK) by analyzing the establishment in 2005 of a new organizational form for social enterprise - the Community Interest Company (CIC). The CIC is a legal structure designed to permit trading for social purpose and ensure that company assets are committed to community benefit in perpetuity. The establishment of the CIC legal structure was an important historical event, especially in the UK where the previous new organization legal structure was introduced more than 100 years ago (Nicholls, 2010). How new institutions are instantiated is an important aspect of economy and society (Smith and Teasdale, 2012) and an historical lens enriches our understanding of social economy development in the UK. Moreover, we are only just beginning to understand the impacts of new legal structures for social enterprise on social economies in different countries (Gottesman, 2007; Gupta, 2011; Lasprogata and Cotten, 2003; Rawhauser et al., 2015; Reiser, 2011, 2013; Smiddy, 2010). The research is guided by the question when, why and how was a new legal structure for social enterprise established in the UK?