This chapter focuses on what has become known as the psychometric or nonrepresentational approach to measurement. It considers the issues traditionally discussed under the heading of reliability, and reviews several still persistent definitions or types of reliability coefficients. The chapter discusses the problems and misuses of coefficient alpha, the most commonly used psychometric index in social-personality psychology. It suggests the generalizability theory as a broader and more heuristic perspective. The chapter examines issues related to construct validation. It also considers the construct validation as the crucial issue in psychological measurement and includes a broad range of validity evidence, focusing on convergent and discriminant aspects. The chapter describes model testing in construct validation and scale construction. It also focuses on the measurement models in structural equation modeling. The chapter reviews three classical strategies (external criterion, rational-intuitive, and internal-factor analytic) and also suggests an integrated model adopting the construct-oriented approach.