This paper primarily focuses on the family language policy of bilingual Russian-Estonian and Russian-Spanish families in relation to the maintenance of Russian as a heritage language. Its main objective is to identify social factors that either help or hinder this process. In doing so, this paper searches for commonalities and specificities of the mainstream attitudes towards Russian as a heritage language in Estonia and Spain, by analysing the sociolinguistic situation of Russian in both countries and by examining the factors conditioning the maintenance of Russian as a heritage language in family settings. Our research is based on an in-depth analysis of a variety of sources, mainly quantitative statistical and demographic data on self-reported language behaviour and language ideologies in mixed families from Estonia (n = 40) and Spain (n = 40). The main results of our comparative study confirm the general positive attitude towards Russian as a heritage language, but they also highlight an important variability of these attitudes both between countries and within each community. We show that these attitudes directly determine the principles of family language policy, the parents’ strategies to transmit Russian as a heritage language, and the level of proficiency in Russian as a heritage language in the second generation. These results allow us to conclude that, as a heritage language, Russian relies on strong attitudinal support in even small communities, like Estonian or Spanish, but also that its confident transmission should rely on external subsidy.