The family is one of the social structures more resistant to abrupt changes, but in the second half of the twentieth century the European family underwent many important transformations. It is not difficult to identify common trends across many countries in relation to family changes: an increase in the divorce rate, an increase in the number of unipersonal households, the decreasing weight of the polynuclear family and the appearance of new forms of cohabitation. Spain is not alien to these shifts, but the metamorphosis of the Spanish family happened, in comparison to other European countries, very late and very quickly, in parallel with a delayed but accelerated period of industrialisation and economic growth.

The centrality of the family in Spanish life has shown tremendous resilience. The definition of what constitutes a family has evolved, and in the last decade we have witnessed the emergence of two conflicting family models. One, ideologically emanating from the Catholic church or even the standard definitions provided by the United Nations, would consider the family as a unit structured around a married heterosexual couple. The other model, a more liberal approach, departs from an egalitarian view of relationships in the private sphere, and accepts same-sex relationships and less conventional household structures. There is still, in spite of these different approaches, a common view of what essentially constitutes a family: a study of different family associations, of both traditional and liberal views, has identified a common definition of a family as a unit that shares a life project, involves relationships of reciprocity and mutual help and is oriented towards happiness.