Psychologists disagree about the definition of intelligence and how to measure it. This article will discuss the definition of intelligence and how it is measured by comparing and contrasting the two intelligence tests and the two achievement tests chosen from the Mental Measurement Yearbook. The intelligence tests chosen were the Primary Test of Nonverbal Intelligence (PTONI) and the Test of Memory and Learning, 2nd ed., (TOMAL-2) and the achievement tests chosen were the Basic Achievement Skills Inventory ( BASI) and the Differential Ability Scales. , 2nd ed. (DAS-II). Intelligence test measures will be evaluated for reliability, validity, normative procedure, and bias, and then compared with achievement tests. Definition of Intelligence According to Cohen and Swerdlik, (2010), “Intelligence is a multifaceted ability that manifests itself in different ways throughout life, but generally included the skills and abilities to acquire and apply knowledge to reason intelligently. effective and logical, to show good judgment, to be insightful, intuitive, mentally alert and able to easily find the right words and thoughts, and to be able to deal with and adapt to new situations and new types of problems” (p. 277). This definition is very broad but inclusive. Psychology professionals have different definitions and personal biases that make a standard definition difficult. Some professionals believe that intelligence is observable, but others believe that life experiences influence and develop intelligence and inform information for dealing with future situations. Various psychologists, behavioral specialists, and laypeople have different definitions or ideas about what intelligence is. A widely accepted definition... at the heart of the article......ogy.about.com/od/cognitivepsychology/p/intelligence.htmCohen, RJ, Swerdlik, ME (2010). Psychological testing and evaluation: An introduction to testing and measurement (7th ed.). New York: McGraw Hill.Ehrler, D. J., & McGhee, R. (2008). Primary test of nonverbal intelligence. Retrieved from EBSCOhost.Elliott, C. (2007). Differential Ability Scales-Second Edition. Retrieved from EBSCOhost.Gredler, G. R. (1999). The Twelfth Yearbook of Mental Measurements/The Thirteenth Yearbook of Mental Measurements (Book). Psychology in Schools, 36(1), 79. Retrieved from EBSCOhost.Net Industries and its licensors. (2011). Standardized racial difference testing and race. Retrieved from http://social.jrank.org/pages/529/Racial-Differences-Standardized-Tests-Race.htmlReynolds, C. R., & Voress, J. (2007). Memory and learning tests, second edition. Retrieved from EBSCOhost.