The purpose of this article is to introduce the inspection-time measur
e to the wider psychological community. Inspection time is, to date, t
he only single information-processing index that accounts for approxim
ately 20% of intelligence-test variance. We argue that inspection time
, because of its much-replicated correlation with IQ and its potential
for theoretical tractability, has more potential for our understandin
g of individual differences in cognitive ability than other indexes of
human information processing. The nature of inspection time and its m
easurement are described, studies correlating inspection time and IQ-t
ype test scores are summarized, and the difficulties of explaining thi
s correlation are highlighted.