The 24-item Physics Metacognition Inventory was developed to measure physics students' metacognition for problem solving. Items were classified into eight subcomponents subsumed under two broader components: knowledge of cognition and regulation of cognition. The students' scores on the inventory were found to be reliable and related to students' physics motivation and physics grade. An exploratory factor analysis provided evidence of construct validity, revealing six components of students' metacognition when solving physics problems including: knowledge of cognition, planning, monitoring, evaluation, debugging, and information management. Although women and men differed on the components, they had equivalent overall metacognition for problem solving. The implications of these findings for future research are discussed. (Contains 3 tables.)