From the 3rd paragraph of art. 226 of the Federal Constitution of 1988, it is possible to visualize the ?União Estável? (cohabitation), also called common-law marriage, as a fact existing between two people, of different sexes and free to marry, living together, as if married were characterizing a family entity. The lawmaker refrained from conceptualizing rigidly the cohabitation, leaving to the judge - in each concrete case - the task of analyzing it and recognizing it or not. Therefore, it is a factual situation, establishing an affective bond between a couple, intending to live as if they were married. Cohabitants is the expression consecrated in the Civil Code to designate the subject of the cohabitation, eliminating the prejudice that the word ?concubinato? brought with it. the stable union is subject to some essential elements: (i) gender diversity; (ii) stability; (iii) publicity; (iv) continuity; (v) absence of marital impediments. These five elements need to be connected to a main element, which is the spirit of constituting family (coexistence more uxorio). Cohabitation expands its consequences in different fields, projecting itself in the patrimonial relations, of economic nature, and also in the personal relations, domiciled in the internal scope of the relation maintained by the couple and very much resemble the effects of the marriage. In spite of the distinctions with marriage, not only is it possible to convert a cohabitation into a marriage, but also to consider the possibility of characterizing homosexual unions as cohabitations for legal effects.