Linguistic Approaches to Bilingualism 7:5 (2017), 514–553. doi 10.1075/lab.15007.mei issn 1879–9264 / e-issn 1879–9272 © John Benjamins Publishing Company Bi-directional cross-linguistic inﬂuence in bilingual Russian-Hebrew children Natalia Meir, Joel Walters and Sharon Armon-Lotem Bar-Ilan University is study examines cross-linguistic inﬂuence of L1 on L2 and L2 on L1 and the extent to which age of L2 onset (L2 AoO) is linked to the acquisition of morpho-syntactic properties in both languages of bilingual children who acquire L1-Russian as a heritage language and L2-Hebrew as a majority language. Our investigation of L1-L2 inﬂuence focuses on morpho-syntactic features, whose conﬁgurations vary in Russian and Hebrew. Deﬁniteness is realized in Hebrew (but not in Russian), aspect is selected in Russian (but not in Hebrew), and [ACC] case is realized in both languages (but the mapping is diﬀerent across the two languages); ﬁnally, the features of [Person], [Number] and [Gender] are mapped onto verbal inﬂections in both languages. A total of 110 Russian- Hebrew bilingual children aged 5;5–6;5 with varying ages of L2-Hebrew onset (0–60 months), 20 Hebrew-speaking monolinguals and 20 Russian-speaking monolinguals participated. Results demonstrate cross-linguistic inﬂuence, showing that it is bi-directional (L1 on L2 and L2 on L1). e patterns of cross- linguistic inﬂuence were similar: bilinguals performed similarly to monolinguals on features, with similar conﬁgurations in L1 and L2 (i.e., subject-verb agree- ment) but performed lower for properties realized diﬀerently in L1 and L2 (i.e., [DEF] articles in L2-Hebrew; [PERF] aspect and [ACC] case inﬂections in L1- Russian). e results also showed an eﬀect of L2 AoO on the acquisition of both L1 and L2. Children with earlier AoO to L2-Hebrew (before 24 months) achieve better mastery in L2-Hebrew and performed lower in L1-Russian. Conversely, later AoOs to L2, led to better mastery of L1 and weaknesses in the acquisition of L2. Findings are discussed in light of the Feature Re-assembly Hypothesis. Keywords: child heritage speakers, cross-linguistic inﬂuence, age of L2 onset (L2 AoO), morpho-syntax, case, aspect, deﬁniteness, subject-verb agreement, Russian, Hebrew