The history of Spain is not usually associated with liberalism or constitutional innovation by most English or American historians. This paper provides a brief history of the rise of liberalism in Spain and uses the Constitution of 1812 as a window into the political liberalism of Spain in the early nineteenth century. That constitution makes it clear that the constitutional political economy and political liberalism were well advanced in Spain at the beginning of the nineteenth century. Had the king accepted his greatly reduced authority under the Cadiz Constitution and foreign powers not intervened as they had in France, Spanish history for the next two centuries might have been very different.