Expertise refers to the psychological processes that underlie the superior achievement of experts, who are typically defined as those who have acquired special skills in, or knowledge of, a particular subject through professional training and practical experience. The term expert has a long history that can be traced all the way back to the training of skilled craftsmen in the guilds of the Middle Ages. At that time most of the professional skills, such as shoemaking, tailoring, and weaving, were taught through an apprentice system, whereby adolescents worked for a master in return for being allowed to observe and learn the skills of the trade. When the apprentices had sufficiently learned the necessary skills enabling them to work independently, they often left the master and traveled around the country as journeymen to find work. This allowed them to further develop their skills until they had reached a level of understanding and mastery of their craft to attain expert status. Eventually they would have accumulated skills to produce master pieces, which would meet the quality standard set by masters in the guild, who would give them permission to set up their own shop and accept their own apprentices.

ExpertiseOver time, the terms master and expert have been extended and are today used to describe a wide range of highly experienced professionals, such as medical doctors, accountants, teachers, and scientists. Its usage has even been expanded to include any individual who has attained superior performance by instruction and extended practice, ranging from birdwatchers to pianists, golf players to chess players.

When elite ice skaters, chess players, and musicians demonstrate outstanding skill in public, their performance often looks extremely natural and surprisingly effortless. To the casual observer, these exhibitions appear so extraordinary that it seems unlikely that most other performers, regardless of the amount or type of training, will ever achieve similar performance levels. It is tempting to attribute these amazing achievements to the performer’s unique innate talent, deemed necessary for such superior performance achievement. However, when scientists began measuring the experts’ presumed superior powers of speed of thought, memory, and intelligence with psychometric tests, no general superiority was found; the demonstrated superiority was limited to particular types of stimuli and activities. For example, the superiority of the chess experts’ memory was constrained to regular chess positions and did not generalize to other types of materials. Not even IQ could distinguish the chess masters among chess players nor the most successful and creative among artists and scientists. Recent reviews show that (a) measures of general intelligence do not reliably distinguish those who will succeed in a domain, (b) the superior performance of experts is often specific to a domain of activity and does not transfer outside their narrow area of expertise, and (c) individual differences between experts and less proficient individuals nearly always reflect attributes acquired by the experts during their lengthy training.

The pioneering research on the thought processes at the highest levels of performance studied expert and world-class chess players. To gain insight into differences in speed and structure of thinking, the chess players were instructed to think aloud while selecting the next move for unfamiliar chess positions. The world-class players did not differ from the less skilled players in the speed of their thoughts or the size of their basic memory capacity. The superior ability of the world-class players to generate better moves was based on their extensive experience and knowledge of patterns in chess. In the first formal theory of expertise, William G. Simon and Herbert A. Chase proposed that experts with extended experience learn a larger number of complex patterns and use these new patterns to store new knowledge about which actions should be taken in similar situations.

According to this influential theory, expert performance is viewed as the result of skill acquired with gradual improvements of performance during many years of experience in a domain. With further experience and instruction, aspiring experts acquire more knowledge about the domain, so it is tempting to assume that the performance of experts improves as a direct function of increases in knowledge through training and extended experience. However, there are now many demonstrations that extensive domain knowledge does not necessarily result in superior performance. For example, the outcomes of psychological therapy do not improve as a function of the length of training and professional experience of the therapist. Similarly, the accuracy of decision making, medical diagnosis for common diseases, and the quality of investment decisions do not improve with further professional experience. More generally, the number of years of work and experience in a domain is a poor predictor of attained level of professional performance.

In a pioneering study, Benjamin Bloom and his colleagues studied the developmental history of scientists, athletes, and artists who had won international prizes for their outstanding achievements. These elite performers did not acquire their performance from regular activities within their respective domains, in which most amateurs participate, but they were identified early and given special opportunities to study and train in the best educational environments. Their families provided substantial financial and emotional support to allow them to focus fully on the development of their performance. Bloom’s influential research demonstrated the necessity for extended training in the best training environments to reach the highest levels of performance.

Subsequent research by K. Anders Ericsson, Ralf Krampe, and Clemens Tesch-Romer analyzed the effects of different types of experience on the improvement of performance. They found that in activities in which individuals had attained an acceptable level of performance, such as recreational golf and many professions, even decades of continued experience was not associated with improvements in performance. The aspiring expert performers, who were able to keep improving their performance for decades, were found to seek out particular kinds of experiences involved in deliberate practice—that is, activities designed, typically by a teacher, for the sole purpose of effectively improving specific aspects of an individual’s performance. In support of the critical role of deliberate practice, expert musicians differing in the level of attained solo performance also differed in the amounts of time they had spent in solitary practice during their skill development, which totaled around 10,000 hours by age 20 for the best experts, around 5,000 hours for the least accomplished expert musicians, and only 2,000 hours for serious amateur pianists. Many subsequent studies have found that the accumulated amount of deliberate practice is closely related to the attained level of performance of many types of experts, such as surgeons, radiologists, musicians, dancers, chess players, and athletes.

The recent advances in our understanding of the concepts, knowledge, and skills that mediate experts’ superior performance come from studies in which experts are instructed to think aloud while they complete tasks that are representative of essential activities in their domains. Other advances come from researchers who record where the experts are looking while they perform the same type of tasks. Finally, important advances result from attempts to build computer programs (expert systems) that are capable of regenerating the performance of human experts.

These studies that monitor the experts’ cognitive and perceptual processes have found that the differences between experts and less skilled individuals are not merely a matter of the amount and complexity of the accumulated knowledge; they also reflect qualitative differences in strategies, organization of knowledge, and representation of problems. During the extended development of their performance abilities, experts acquire domain-specific memory skills that allow them to use long-term memory (long-term working memory) to dramatically expand the amount of information that can be kept accessible, while the experts plan and reason about alternative courses of action in a situation. The superior structure of the experts’ mental representations allow them to adapt to changing circumstances as well as anticipate future events, so the expert performers can respond with impressive speed without any innate neurological advantage. The same acquired representations have been found to allow experts to have the ability to monitor and self-regulate their own performance so that they can keep improving their own performance by designing their own training.

In this way, experts’ superior skills are primarily acquired, and expertise is developed through mental and physical adaptations to the demands of the task domains.


  1. Bloom, B. S. (Ed.). (1985). Developing talent in young people. New York: Ballantine Books.
  2. Ericsson, K. A. (2002). Attaining excellence through deliberate practice: Insights from the study of expert performance. In M. Ferrari (Ed.), The pursuit of excellence in education (pp. 21-55). Mahwah, NJ: Erlbaum.
  3. Ericsson, K. A., Charness, N., Feltovich, P., & Hoffman, R. R. (Eds.). (2006). Cambridge handbook of expertise and expert performance. Cambridge, UK: Cambridge University Press.
  4. Ericsson, K. A., & Lehmann, A. C. (1996). Expert and exceptional performance: Evidence on maximal adaptations on task constraints. Annual Review of Psychology, 47,273-305.
  5. Simon, H. A., & Chase, W. G. (1973). Skill in chess. American Scientist, 61, 394-403.