This article reports on an empirical exploration of the relations and strengths among Turkish grades 9-11 students' (n = 209) personal epistemologies (justification of knowledge, certainty of knowledge, source of knowledge, development of knowledge), self-regulated learning (extrinsic motivation, intrinsic motivation, rehearsal, elaboration, organization, critical thinking, metacognitive self-regulation), and achievement in physics (course grades). Established instruments were used to collect data on these students' beliefs about knowledge and components of self-regulated learning (SRL) such as goal orientations (extrinsic and intrinsic motivation) and learning strategies, critical thinking, and metacognitive regulation. Results from structural equation modeling revealed that students' personal epistemologies directly influenced their motivation (extrinsic and intrinsic goal orientations), rehearsal and organization strategies, and metacognitive self-regulation to learn physics. Furthermore, students' personal epistemologies indirectly (mediated through motivation beliefs) influenced rehearsal, elaboration and organization strategies, critical thinking, and metacognitive self-regulation to learn physics. Students' ideas about knowledge and knowing about the source and development of knowledge significantly contributed to students' self-regulatory skills and physics course grade. Implications and future directions are discussed.