The term "Heritage Language" (HL) refers to a language spoken at home that is not the Majority Language (ML) of the society. HL speakers, while acquiring the HL in childhood, often show varied linguistic abilities compared to the baseline spoken by 1st-generation immigrants. This project (2021-2024) investigated HL-Russian in contact with Hebrew and English, focusing on three developmental trajectories: incomplete acquisition, attrition, and the emergence of new varieties. It also examines mechanisms behind HL divergences, including restructuring due to ML influence and grammar shrinkage. By comparing HL-Russian across these typologically distinct MLs, the study explores the impact of ML features on HL grammar, particularly in morphology, and considers external factors like input, literacy, and community dynamics. The findings aim to deepen understanding of how bilingual grammars evolve and inform efforts to support HL maintenance.