This chapter shows that economic development since the late nineteenth century provoked considerable transformations in the allocation of economic activity at the regional level, which are not depicted in the national histories of Portugal. The analysis of regional economic growth may also help to explain the economic performance of Portugal. In this sense, initial regional per capita income levels at the end of the ineteenth century may be closely related to natural endowments, such as soil fertility, weather conditions, mining resources and access to the rivers. In order to analyse the long-term evolution of regional inequality and its determinants, the chapter analyses regional GDP figures from 1890 to 1950, which are linked afterwards with data published in official sources, already available from 1960 onwards. Portugal’s regional inequality in the long term followed an inverted U-curve, with a peak around the 1970s, a few decades later than the peak observed in Spain, and later than in other countries.