The study of expertise is based on the premise that experts in different domains follow a similar path of acquisition and development. This article distinguishes two research approaches to the study of expertise. The traditional approach assumes a steady progression from novice to expert as a function of training as well as years of experience often without measures of reproducible skill. A second and more recent one focuses on the identification of individuals with reproducibly superior performance for representative tasks that capture expertise in the domain. The focus of this review is on the latter, namely the expert-performance approach. The article describes how superior performance can be captured by standardized tasks, and how analyses of that superior performance can identify superior abilities, cognitive mechanisms, and physiological adaptations. The last part of the article reviews how deliberate practice and training can lead to the acquisition of complex mechanisms and physiological adaptations, which in turn can explain the experts’ attained superior performance. The review is concluded with a discussion of future directions of studies of expert performance and the challenges in understanding the development of general abilities and the motivation to engage in sustained daily deliberate practice.