1 Oneness versus Diversity in Legal and Economic Institutions: The Spanish Stock markets, 1831-1936. Juan Carlos Rojo Cagigal † and Stefan Houpt † Emails: jcrojo@clio.uc3m.es; shoupt@clio.uc3m.es February 15, 2011 Abstract The paper analyses the development of regulation and microstructure of stock markets in Spain until the Spanish Civil War. It examines the transfer of French legislation in the 1830s and its implications for the final configuration of the regulatory framework. It studies the choice and bargaining processes, the law enforcement and the configuration of a mixed system: an étatiste model in Madrid and Bilbao, a free market in Barcelona, and small traditional markets in the rest of the country. It shows that different models of financial intermediation could coexist to meet the different needs of each specific region. Keywords: legal transplant, regulation, stock exchange JEL Classification: N24, N44 † Both acknowledge financial support from Spanish Ministerio de Educación y Ciencia proyecto SEJ2006- 08188/ECON and ECO2009-13331-C01-01. Houpt also acknowledges financial support from the Spanish Ministry of Education Subprograma de Estancias de Profesores e Investigadores Séniores en Centros Extranjeros de Enseñanza Superior e Investigación PR2010-0104 and from the Spanish Ministerio de Ciencia e Innovación proyecto «Consolidating Economics» within the Consolider-Ingenio 2010 programme. Houpt would also like to thank the History Department at UC San Diego and specially Pamela Radcliff for their kind sabbatical year invitation. Useful comments have been received at the EuroHistock Conference in Madrid. The usual disclaimer applies to the errors that may remain.