The focus in this chapter is on reliability and validity, two topics that have generated many papers and books. As it is nearly impossible to review all of the developments in a single book chapter, we aim to provide a broad overview of recent developments in reliability and validity theory and periodically provide more detail to demonstrate the vast array of measurement methodologies and approaches currently available to aid us in illuminating our understanding of social and behavioral phenomena. We will view these developments through a statistical modeling lens to highlight the consequences of choosing