Epistemological beliefs are subjective theories on the structure and acquisition of knowledge. Using data collected in the final year of high school (Time 1) and early in the college career (Time 2) as part of a large-scale longitudinal study, we examined the relationship of beliefs in the certainty of knowledge with school achievement and choice of college majors in Germany. In line with our hypothesis, students high on certainty beliefs showed lower school achievement at Time 1, even when controlling for indicators of intelligence and family background. Certainty beliefs also predicted the choice of future fields of study at college (self-selection hypothesis) and were shaped by enrolment in specific fields of study at college (socialization hypothesis).