This study examines the relationship between principals' leadership and student achievement. Based on the Programme for International Student Assessment (PISA) 2015 United States data, a two-level hierarchical linear model (HLM) with students nested within principals and schools was applied. The findings showed (a) that principals' rating of their own overall leadership was statistically negatively related to student achievement, (b) that among the four subscales of principal self-rated leadership, instructional leadership was statistically positively related to student achievement, while leadership for teacher development was negatively related to student achievement and (c) that principal leadership's effect on student achievement was moderated by school contextual variables. Implications of the findings were discussed.