The library advances communicational processes within the society and explores the user's need for information and literature. Children's libraries operate as a network, which includes the space, programs, anthologies, competent children librarians, thus having one of the most significant roles in the advancement and promotion of reading literacy. Literacy, as well as reading, is a fundamental process in the development of an individual and determines the extent to which an individual will acquire the ability to successfully manage himself in a wealth of information. Based on the premise that reading with pleasure is the basis for further development of the reader, libraries study, investigate, exchange and adapt knowledge, experience and ways in which to investigate the reader, and from an early age on try to encourage reading, create a habit of reading and facilitate the development of a love for reading in young readers. Developing reading literacy is preceded by the development of the reading process, in which, according to author Čudina-Obradović, building blocks of literacy are of great importance and will thus be discussed in this paper. Research in Croatia has shown that one of the institutions most trusted by parents in high percentage are libraries, which can be distinguished according to the purpose and content of their library fund national, public, school, university, higher educational, general scientific, and special libraries. In this paper, the emphasis will be placed on public and school libraries and their mutual complementarity in the overall process of reading literacy development.