POSOFIS is a research group focus on the study of power, society and taxation system in the Crown of Castile between the 13th and the 18th centuries. In a more specific way, the studies tackled are focus on the North of the Iberian Peninsula, paying critical attention to the Autonomous regions of the Basque Country, Cantabria, Asturias and Galicia. The existing narrow relationship between the political power and its financial sources is the main thread of research group members. It is known that the taxation system is an essential tool in order to guarantee the proper running of the public political organizations.

The historical research carried out tries to understand better the evolution and the development of the public administrations located in the geographical area being studied. But this is impossible without examining the social context where they were inserted. Therefore, it is essential to deepen into the study of the social sectors that were involved in the fiscal and financial business, their professions, social organizations, ways of life, beliefs and political position. In short, it is a matter of understanding the origins of the contemporary public administrations and of contributing to the cultural education of the current society.