Individual differences in processing speed and executive attention have both been proposed as explanations for individual differences in cognitive ability, particularly general and fluid intelligence (Engle et al., 1999; Kail & Salthouse, 1994). Both constructs have long intellectual histories in scientific psychology. This article attempts to describe the historical development of these constructs, particularly as they pertain to intelligence. It also aims to determine the degree to which speed and executive attention are theoretical competitors in explaining individual differences in intelligence. We suggest that attention is the more fundamental mechanism in explaining variation in human intelligence. (PsycInfo Database Record (c) 2024 APA, all rights reserved).