This study analyzes similarities and differences in students' motivation to learn based on nationally representative samples of 15-year-olds from 26 countries. Scales of extrinsic and intrinsic motivation proved to be equivalent across countries but there seems to be a shift in meaning at the country level. Focusing on functional relationships within countries, the results show that in most countries, extrinsic and intrinsic motivation vary independently of each other and are by no means antagonistic. On the contrary, both are important in the regulation of actual learning behavior: Whereas interest in reading mostly showed direct effects on students reading performance, instrumentally motivated students seemed to perform better only because of their frequent use of control strategies during learning.