Teachers' general pedagogical/psychological knowledge (PPK) can be defined as the knowledge needed to create and optimize teaching-learning situations across subjects, including declarative and procedural knowledge of classroom management, teaching methods, classroom assessment, and student heterogeneity. Although PPK is thought to be an important aspect of teacher quality, it has seen little empirical investigation--largely because no direct and valid measure of PPK has previously been available. Study 1 describes the development of a 39-item measure using multiple-choice items, short-answer items, and video-based items to assess PPK. Experts rated the items to be relevant for teaching and domain general. Study 2 provides further evidence for the measure's validity. Data obtained from 746 German teacher candidates supported the hypothesized nomological network of PPK; the measure was sensitive to differences between groups; and variations in PPK did not overlap to any great extent with variations in discriminant constructs such as general reasoning abilities, personal beliefs, and domain-specific knowledge. Furthermore, PPK was positively associated with indicators of instructional quality from the students' perspective. (Contains 6 tables, 2 figures and 4 footnotes.)