Conscientiousness and domain-specific competence beliefs are known to be highly important predictors of academic effort and achievement. Given their basis in distinct research traditions, however, these constructs have rarely been examined simultaneously. Three studies with 571, 415, and 1,535 students, respectively, found a moderate association between conscientiousness and competence beliefs, but competence beliefs meaningfully predicted both conscientiousness and academic effort, irrespective of how academic effort was measured (student report or diary data). The associations of competence beliefs with academic effort were highly domain specific, whereas conscientiousness was predictive of academic effort across a wide range of academic subjects. Conscientiousness and competence beliefs were also associated with academic achievement. Cognitive ability, although associated with academic achievement, only loosely predicted academic effort