Letters of recommendation are used extensively in academic admissions and personnel selection. Despite their prominence, comparatively little is known about their predictive power for multiple outcomes. This meta-analysis combine the existing literature for college grade point average (GPA), academic outcomes of GPA, performance ratings, degree attainment, and research productivity for nonmedical school graduate programs, and GPA and internship performance ratings for medical school students. Intercorrelations with other commonly used predictors are also estimated and used to estimate incremental predictive power. Overall, letters of recommendation, in their current form, are generally positively but weakly correlated with multiple aspects of performance in post-secondary education. However, letters do appear to provide incremental information about degree attainment, a difficult and heavily motivationally determined outcome.