Retrieval practice is well-established as a powerful tool for reinforcing long-term learning. Most previous research has concentrated on the effectiveness of overt retrieval, involving recalling information from memory and generating overt responses by writing, typing, or speaking aloud the retrieved information. Here we ask whether covert retrieval, involving mentally retrieving information without producing overt responses, can enhance learning and consolidate long-term memory, and whether it does so as effectively as overt retrieval. The current meta-analysis integrated data from 2560 participants across 18 studies to investigate the magnitude, boundary conditions, and underlying mechanisms of the covert retrieval effect and the relative efficacy of overt and covert retrieval. The results showed that covert retrieval enhances learning to a small but significant extent (g = 0.23), and its effectiveness is moderated by several factors including provision of corrective feedback, control strategy, and retention interval. The results support the additional exposure and desirable difficulty theories to jointly account for the covert retrieval effect. The meta-analysis also found that overt retrieval is more effective than covert retrieval (g = 0.17), with the effect size of this additional benefit being moderated by the mode by which covert retrieval is performed. The results support the truncated search and desirable difficulty explanations of the relative benefit of overt compared to covert retrieval. Overall, the documented findings provide practical implications for optimizing learning and teaching practices and highlight several important directions for future research.