This chapter provides a broad review of theories and research on intelligence with particular emphasis on its importance in the workplace. Psychometric theories of intelligence, beginning with Spearman and concluding with Carroll, are described. Spearman's (1904) original theory emphasized the importance of general cognitive ability, which he denoted as
g
; after a century of research and controversy, Carroll's massive reanalysis of the available data placed
g
at the apex of a three‐stratum model. The information‐processing approach to intelligence and the neuropsychological perspective is also summarized. Then research on the relation of intelligence and performance is reviewed. Laboratory studies of skill acquisition, as well as field studies of workers, clearly show the critical role of intelligence for job performance. Interestingly, it has been argued that specific facets of intelligence, such as reading comprehension and quantitative reasoning, provide little incremental validity over general cognitive ability. A limitation on this line of argument is that it has focused on the prediction of task performance; effectiveness in interpersonal activities that contribute to organizational effectiveness has been considered to a lesser extent. Broadening the conceptualization of performance to include both task performance and contextual performance suggests that social intelligence or situational judgment may add substantially to the validity of prediction. Finally, avenues for future research are described.