Living in a cohabitation union is a more and more popular way of life in the contemporary societies. Changes in family behaviour and formation, such as increases in births outside of marriage, age at first marriage, and divorce have occurred in western countries with different paces and intensity as the elements of Second Demographic Transition (SDT). The aim of the article is to investigate the main determinants which influence attitudes towards living in a cohabitation union in two catholic countries: Spain and Poland. Using the European Social Survey conducted in Poland and Spain in two different moments 2006 and 2018, we carried out ordinal regression models in order to confirm which variables affect more the choice of this union. The results showed that educational level, placement on the left-right scale and religion are the prevailing predictors in both countries and both periods of time, but with different intensities, being greater for the Polish case.