Background and Aims: Epidemiological studies have provided invaluable insight into the origin and impact of low language skills in childhood and adolescence. However, changing terminology and diagnostic guidelines have contributed to variable estimations of the prevalence of developmental language difficulties. The aim of this review was to profile the extent and variability of low language prevalence estimates through a systematic review of epidemiological literature. Methods: A systematic review of the empirical research (August 2022) was undertaken to identify studies that aimed to estimate the prevalence of low language skills in children (<18 years). A total of 19 studies published between 1980-2022 met inclusion criteria for review. Results: Studies reported prevalence estimates of low language skills in children between 1 and 16 years. Estimated rates varied from 0.4% to 25.2%. More stable estimations were observed in studies of children aged 5 years and older and those that applied updated diagnostic criteria to performance on standardised assessments of receptive and expressive language. Conclusions and Implications: The estimated prevalence of low language skills in childhood varies considerably in the literature. Application of updated diagnostic criteria, including the assessment of functional impact, is critical to inform advocacy efforts and govern social, health and educational policies.