<p>Research on extensive reading (ER) has quite consistently highlighted its impact on second/foreign language learning. However, it remains unclear what the exact components of ER are that make it profitable. In practice, there appears to be variation in the application of key elements of ER, and programs vary in the kinds of additions they make to these elements. The aim of this meta-analysis was to assess the impact of ER on second/foreign language learning and to examine which key elements and additions to ER contribute to its success. The effects of ER proved to be positive across all included language domains (reading comprehension, vocabulary, decoding/fluency, motivation, writing, oral proficiency, general language proficiency) and target populations, with effect sizes ranging from small to medium. Variability in effect sizes was affected by two intervention characteristics: when learners’ text choice was limited and when some form of accountability was included, effects were larger than when these elements were absent. Additionally, effect sizes were larger when the members of a sample had different first languages. This meta-analysis supports the assumption that encouraging second/foreign language learners to engage in sustained, independent, and self-selected reading promotes a range of second/foreign language skills. Since ER seems to be underutilized as an educational approach in second/foreign language teaching, our outcomes can be taken as a stimulus to promote its use. At the same time, further research is needed, both in the context of second language learning and in younger populations.</p>