The current chapter focuses on philosophical and scientific developments in the assessment of teacher knowledge. The goal is to provide an overview of major developments in the assessment of teacher knowledge and to illustrate those developments with representative and significant efforts. The authors made evaluative judgments of importance based on their presence in practice, their contributions to policy, and/or their contributions to the research base on teacher assessment. The authors conducted their literature review for this chapter by first searching for all relevant papers that addressed teacher knowledge. The authors then selected from this very broad literature articles and examples that they judged to have had significant influence and impact on assessments of teacher knowledge and used these examples to support the conceptual argument and framework of the chapter.