This chapter focuses on test security in the context of computer-based testing (CBT). It presents a validity perspective on test security, discusses the case for security planning, provides an outline of the major components of a comprehensive security plan, and explores the practical issue of budgeting for test security. Security during test administration actually begins well before the actual administration with the processes in place to ensure that the examinees who register to take an examination are qualified to do so. Licensure and certification boards routinely have in place criteria that must be met for a candidate to be eligible to sit for a credentialing examination. These policies should be clearly articulated, disseminated to potential examinees, and routinely monitored for compliance. The chapter focuses on computer-administered tests; we note that paper-based test forms present a major threat to the security of a testing program because each page that falls into the wrong hands includes verbatim copies of live test items.