In Latvian linguistics the studies of the Latvian language of bilingual children are only at an early stage, certain language facts, phenomena, etc. are being examined, but the Latvian language of bilingual children is not being analysed in large-scale. This is an urgent field of multidirectional scientific activity, in which researchers have to solve many problems - both simultaneous and sequential bilingualism development at preschool and primary school age, the bilingualism of the Latvian children and the children of other nationalities in Latvia, the acquisition of the Latvian language at preschool age and creating the related linguistic and didactic bases as well as the psycholinguistic aspect of the development of this age children's speech and language learning, and so forth. The research problem is related to the necessity to solve theoretical and practical problems of applied linguistics regarding the acquisition of the Latvian language as a second language by the children at preschool age. This Doctoral Thesis is an interdisciplinary study in applied linguistics, which deals with the correlation of the theories of contemporary linguistics and the second language acquisition with the child's linguistic environment, also evaluating the Latvian language curricula, tools and the second language acquisition practice in a preschool educational institution. The theoretical basis of the Thesis research consists of the theories of linguistics and language learning, centered on the child language and the question, what affects the development of the child L2. The research problem determines the necessity of the research of the theme of the Doctoral Thesis “The Latvian Speech Specifics of the Russophone Bilingual Preschoolers”. The research is important for promoting the acquisition of the child second language and developing this field of research in Latvia. The subject of the research is the Russophone preschoolers' command of the Latvian language as a second language and the types of errors that are characteristic for the Russophone preschoolers' Latvian speech at the level of phonetics, grammar and vocabulary. The goal of this Doctoral Thesis is to analyze the Russophone preschoolers' Latvian language at the level of phonetics, grammar and vocabulary based on the theory of linguistics, applied psycholinguistics and sociolinguistics, to systematize the speech errors of the Russophone preschoolers' L2 and to develop recommendations for the acquisition and development of L2 at preschool age. The scientific aspect of the research provides for gaining a theoretical understanding of the process of acquisition of phonetics, grammar and vocabulary in the child second language in order to find out the role of the previous theoretical researches and their appropriateness for achieving the goal. In turn, the practical aspect of the research is related to the improvement of the Latvian language as the L2 teaching theory and practice, so that the experience acquired and the results summarized in the study can be used to organize the study process of the second language adapted to the child's needs and the situation in Latvia.