Variation in intelligence has been one of the most studied topics in psychology for many decades (Geary, 2005;Hunt, 2011;Lubinski, 2004). Because people frequently assume that assessments of intelligence (and similar tests of cognitive ability) are the quintessence of good thinking, one might assume that such measures would serve as proxies for judgment and decision-making skills. It is important to understand why such an assumption would be misplaced.Judgment and decision making are more properly regarded as components of rational thinking, and people often fail to recognize that rationality and intelligence (as traditionally defined) are two different things. In scientific psychology, intelligence definitions derive from performance on established tests and cognitive ability indicators. Statistical study of this performance yields a scientific concept of general intelligence, usually symbolized by g; a concept of fluid intelligence (Gf); and a concept of crystallized intelligence (Gc). The latter two concepts refer to the Cattell/Horn/Carroll (CHC) theory of intelligence-as close as there is to a consensus view in the field of intelligence research (Carroll, 1993;Horn & Cattell, 1967). Sometimes called the theory of fluid and crystallized intelligence (symbolized Gf/Gc theory), this theory posits that tests of mental ability tap a small number of broad factors, of which two are dominant. Gf reflects reasoning abilities operating across of variety of domains-in particular, novel ones. Gf is measured by tasks of abstract reasoning such as figural analogies, Raven Matrices, and series completion (e.g., What is the next number in the series 1, 4, 5, 8, 9, 12, __?). Gc reflects declarative knowledge acquired from acculturated learning experiences and is measured by vocabulary tasks, verbal comprehension, and general knowledge measures. The two dominant factors in the CHC theory reflect a long history of considering two aspects of intelligence: intelligence as process (Gf) and intelligence as knowledge (Gc). The IQ-test components that measure Gf do not assess judgment and decision making and neither do the IQ-test components that measure Gc. In short, no components of currently popular IQ tests measure aspects of rationality.Distinguishing between rationality and intelligence thus helps explain how people can be, at the same time, intelligent and irrational (Stanovich, 2009). As such, researchers need to study separately the individual differences in cognitive skills that underlie intelligence and the individual differences in cognitive skills that underlie rational thinking because they are conceptually and empirically different.