Based on the first long-term whole-population analysis of British small business, it uses novel methods to identify from the 10-yearly population census the two to four million people per year who operated businesses in the period 1851–1911. Using big data analytics, it reveals how British businesses evolved over time, supplementing the census-derived data on individuals with other sources on companies and business histories. By comparing to modern data, it reveals how the late-Victorian period was a ‘golden age’ for smaller and medium-sized business, driven by family firms, the accelerating participation of women and the increasing use of incorporation as significant vehicles for development. A unique resource and citation for future research on entrepreneurship, of crucial significance to economic development policies for small business around the world, and above all the key entry point for researchers to the database which is deposited at the UK Data Archive, this major publication will change our understanding of the scale and economic significance of small businesses in the nineteenth century.