Over the past decade several landmark studies have advanced our scientific understanding of decision-making skill, its measurement, and its acquisition (i.e. Skilled Decision Theory). Here we present an integrative review of skilled human decision-making in experts and non-experts, with emphasis on four emerging insights. (1) Among non-experts, normatively superior decision making is associated with a domain- general skill that has largely been neglected in research on general intelligence. (2) Statistical numeracy tests (i.e. assessments of practical probabilistic reasoning) tend to be the strongest single predictors of general decision-making skill across wide-ranging numeric and non-numeric judgments and decisions (www.RiskLiteracy.org). (3) The superior decision-making exhibited by experts and non-experts primarily reflects specialized knowledge and integrated long-term memory representations that inform adaptive heuristic stra- tegies (i.e. representative understanding rather than rational optimization). (4) High levels of basic cognitive abilities, such as fluid intelligence or attentional control, are not generally required for skilled or expert decision-making.