In 43 countries, 199,097 fifteen-year-olds completed a reading comprehension test and a questionnaire. We analyzed the data using multilevel regressions of Rasch-estimated test scores to test the associations of gender and context on reading achievement among adolescents. In every country, girls outscored boys. Reading enjoyment mediated 42% of the gender effect. No other predictor significantly mediated the gender effect. Log gross domestic product per capita accounted for most of the differences across countries. Family socioeconomic status (SES), schoolmates' family SES, number of books at home, and enjoyment of reading all positively correlated with individual reading achievement. Modeling a student's likelihood of being a poor reader yielded similar results. This study suggests that a comprehensive model of reading achievement must include variables at the country, family, school, and student levels.