The purpose of this study is to examine how validity has been presented in technical and other users' manuals for various editions (i.e., revisions) of the same commercially published test over time. Although the unitary view of validity came to prominence more than 30 years ago and has been embraced in the "Standards for Educational and Psychological Testing" (AERA, APA, & NCME, 2014), questions remain about its application and the utility of putting theory into practice. Previous studies have examined portrayals of validity in journal articles and other publications and found gaps between theory and practice. Research has found the two newest sources of validity evidence in the "Standards"--based on response processes and the consequences of testing--to be particularly lacking. This systematic review of manuals of commercially published tests examines the ways validity coverage has evolved as these 30 tests have been revised over a 72-year period. The tests included in the study were (a) included on a list of assessments school psychologists reported using most and (b) accessible to researchers using the Oscar K. Buros Library of Mental Measurements. This study contributes to the literature by using data from original source material (i.e., test manuals) to ascertain how changes in theory are put into practice. Results suggest the gaps between theory and practice may be narrowing in some areas as citations to the Standards and language consistent with the unitary view have increased. In other areas, however, including evidence based on response processes and consequences as well as references to validity as a property of a test, theory and practice remain divided. The results of this study have implications for testing professionals, test users, educational and psychological measurement scholars, and teachers of assessment courses. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]