The study is a part of two on-going research projects: Cross-linguistic influence and second language acquisition: corpus-based research and Paths in second language acquisition. The project addresses the fundamental question of how cross-linguistic influence, especially the first language (L1) influence determines second language (L2) acquisition (SLA). This project seeks to examine these questions on the bases of learner Estonian and learner Finnish corpora; the first languages involved are Estonian and Finnish. The study has following goals: 1) to examine morphological, morphosyntactical and lexical L1 influence on the acquisition of closely related L2; 2) to investigate relationships between L1 influence and L2 proficiency; 3) to find out factors interacting and competing with L1 influence in the acquisition and processing of L2; 4) to investigate the processing strategies of the learners with closely related L1. The theoretical framework of the study comprises some of the notions of the Competition Model. The methodological starting point is the framework for investigating L1 influence envisioned by Jarvis. For tracing of the development of L2 proficiency the DEMfad model will be used. The project focuses on the written performances of learners which will be compared with the performances of native speakers in literary language corpora. The psycholinguistic reality of cross-linguistic similarity will be ascertained by introspective methods. In order to examine the producing process of the learners, some of the data will be gathered by using the ScriptLog programme combined with retrospective interviews and the thinking-aloud-method. The theoretical significance of this issue lies in the cognitive aspects of SLA, especially the nature and extent of L1 influence which is at least partly different between related and unrelated L1 and L2. The practical significance consists of the needs of language learning and teaching practices in the multilingual situation.