A meta-analysis was performed to investigate the impact of extensive reading (ER) on reading proficiency. This study gathered 71 unique samples from 49 primary studies published from 1980 to 2014 involving a total of 5,919 participants. Effect sizes were generated separately according to two different study designs: experimental-versus-control contrasts and pre-to-post-test contrasts. Small to medium effect was found in both study designs. Moderator analysis showed growing interest in ER in the field over the last 30 years. Also, a higher effect was found in the adults than in the children and adolescents group. English as a foreign language (EFL) settings showed a higher effect than English as a second language (ESL) settings; and web-based stories had a higher effect than paper books. Finally, ER as a part of curriculum showed the highest mean effect among ER types. Suggestions are made on how to implement ER in ESL and EFL settings effectively.