The topic of the thesis is bilingualism and speech development. The central part of the thesis consists of the influence of bilingualism on the development of children's speech and language, which involves presenting various theories on the acquisition of the first and second languages, describing the individual developmental stages characteristic of the acquisition of one or two languages simultaneously, and reviewing existing researched models of simultaneous and sequential bilingualism. The aim of this thesis is to analyze and compare typical speech and language development with the bilingual acquisition process. The analysis of this comparison is shaped and written based on previous research and available literature on monolingualism and bilingualism. At the end of the thesis, as a separate chapter, similarities and differences in research on the influence of monolingualism and bilingualism on developmental language disorders (DLD) are also presented. By comparing theories, developmental stages, and available models, it was revealed that the processes of acquiring the first language and simultaneous acquisition of two languages are almost identical, except that in simultaneous bilingualism, unlike acquiring only one language, there are two separate linguistic systems, which is why children in later stages of development are prone to mixing their two languages. It has also been observed that the final development of the second language greatly depends on the first language and its characteristics.