Knowledge about preschool predictors of later reading comprehension is valuable for several reasons. On a general level, longitudinal studies can aid in generating understanding and causal hypotheses about language and literacy development, both of which are crucial processes in child development. A better understanding of these developmental processes may guide the establishment of effective instruction and interventions to teach reading comprehension that can later be tested in randomized controlled trials. Knowledge about preschool precursors for reading comprehension skills can also aid in developing tools to identify children at risk of reading difficulties. The primary objective for this systematic review is to summarize the available research on the correlation between reading-related preschool predictors and later reading comprehension skills. The following research questions guided this study: (1) To what extent do phonological awareness, rapid naming, and letter knowledge correlate with later decoding and reading comprehension skills; (2) To what extent do linguistic comprehension skills in preschool correlate with later reading comprehension skills; (3) To what extent do domain-general skills in preschool correlate with later reading comprehension skills, and do these skills uniquely contribute to reading comprehension skills beyond decoding and linguistic comprehension; (4) To what extent do preschool predictors of reading comprehension correlate with later reading comprehension skills after concurrent decoding ability has been considered; and (5) To what extent do other possible influential moderator variables (e.g., age, test types, SES, language, country) explain any observed differences between the studies included? A comprehensive search strategy in collaboration with a search information retrieval specialist at the university library was developed based on seven different databases. Findings show that the foundation for reading comprehension is established in the preschool years through the development of language comprehension and code-related skills. Code-related skills and decoding are most important for reading comprehension in beginning readers, but linguistic comprehension gradually takes over as children become older. Taken together, these results suggest a need for a broad focus on language in preschool-age children.