This article analyzes differences in the economic conditions of Spanish regions and their evolution from the point of view of growth theory, emphasizing the convergence process. The characterization of this process varies depending on the type of data we use: the traditional source, elaborated since 1955 by Banco Bilbao-Vizcaya, and the more recent one supplied by the Instituto Nacional de Estadística since 1980, in the form of the Contabilidad Regional. After describing the basic elements of the convergence equation, the paper concentrates on the role played by the productive structure in establishing regional differences, with special reference to the weight of the agricultural sector and to the role of public capital in conditional convergence. A conditional and non-conditional convergence equation is estimated for the 17 Spanish regions, for the period 1955-1991.