Non-pathological first language forgetting is studied by socio- and psycholinguists. Psycholinguistic research relies on the same methodological approaches used in studies of bilingual memory. The present chapter gives a brief overview of theories, tasks, and findings pertaining to this domain of research. The reported empirical study contributes to the existing knowledge of first language (L1) attrition as well as shows a way in which the quantitative and qualitative methods of analysis can be used to provide deeper insight into bilingual memory. Three groups of Russian bilinguals with different second language backgrounds (English, Hebrew, and German) participated in a picture-naming study. Word frequency was found to be a decisive factor in L1 forgetting whereas the length of immigration proved only marginally reliable. Qualitative analysis of the data revealed retrieval failures at the semantic and word-form levels and showed how each of the second languages interfered with successful access of the L1 lexicon.