Background/Context: Because metacognitive knowledge includes knowledge about adequate learning strategies, and because an effective use of learning strategies is associated with higher levels of performance, substantial relationships can be assumed between metacognitive knowledge, strategic behavior, and performance. However, such a pattern of results is rarely found in the research literature. In part, this may be due to inadequate indicators of strategy use. Purpose of study: Prior research showed that high scores on self-reported strategy use were only mirrored in high levels of performance when students had sufficient metacognitive knowledge. To test the cross-country generalizability of the relationship between metacognitive knowledge, strategy use, and reading competence, we analyzed data from the PISA 2009-study, in which similar measures of metacognitive knowledge as well as of students' strategy use were used. Research Design: The study uses a cross-sectional correlational design. It draws on representative samples of fifteen-year-old students from 34 OECD countries taking part in the PISA 2009 study. The relations between students' reading competence scores, their metacognitive knowledge as well as their self-reported use of learning strategies were analyzed. We used correlations, mediation- as well as moderator regression analyses to predict students' reading competence. Findings/Results: Results showed consistently moderate to high correlations between metacognitive knowledge and reading competence. There were also lower, but still significant, relationships between strategy use and both reading competence and metacognitive knowledge. Testing a "mediator model" with strategy use as a mediator resulted in small but significant effects of strategy use as mediator. Assuming that metacognitive knowledge might be a necessary precondition for effective strategy use, the study tested whether it served as a moderator. Results confirmed this moderator effect for many but not all countries. However, across all countries, there was a consistently high effect of metacognitive knowledge on reading competence, independent of the level of self-reported use of strategies. Conclusions/Recommendations: The results are very similar across countries. Taken together, the findings suggest that metacognitive knowledge as measured by a test tapping declarative, conditional and relational strategy knowledge is an important predictor of students' reading competence, and contributes significantly to our understanding of what helps students to become better readers. Metacognitive knowledge captures the prerequisite of adaptive strategic processing of texts. Increasing students' knowledge in this domain is a promising approach when it comes to fostering self-regulated reading.