We review the effectiveness of first-year seminars based on the widely used criteria of first-year grades and the 1-year retention rate. Meta-analytic results indicate that first-year seminars have a small average effect on both first-year grades (k = 89, N = 52,406, d = 0.02) and the 1-year retention rate (k = 195, N = 169,666, d = 0.11). We discuss the implications of these small effects and show that they are meaningful and have important consequences. Results also indicate that the effectiveness of first-year seminars for both criteria is substantially moderated by first-year seminar characteristics (e.g., type of seminar), institutional characteristics (e.g., 2-year or 4-year institution), and study characteristics (e.g., study design). We use these results to make recommendations about the design of first-year seminars that can maximize the positive effect on both the grades and retention of participants.