Executive functioning and intelligence are two umbrella constructs with prominent similarities in the way each is conceptualized and measured. A key characteristic of frontal lobe syndrome post brain injury is relatively intact intellectual capacity with marked executive functioning impairment; however, accumulating research indicates a potentially more complex relationship between these two constructs than was previously suggested. This chapter examines the relationships between executive functioning and intelligence through a review of their definitions and empirical evidence. For this purpose, both psychometric studies and neurophysiologic approaches examining neurologic substrates, brain-lesioned patients and healthy controls were reviewed. Further, research examining the interactions between intelligence and executive functioning in developmental disorders is also discussed. The chapter ends with a discussion of the potential conclusions and implications that can be drawn about the relationship between these two elusive constructs.