Ericsson’s theory of deliberate practice and Chase and Simon’s recognition-action theory both hold that the key to reaching master level performances at chess is to engage at least 10,000 hours of deliberate practice. In addition, Ericsson claims that the primary source of individual differences in chess skill is deliberate practice time. In this dissertation, two studies were conducted to investigate whether deliberate practice or other chess-related experience is sufficient to explain individual differences. Study 1 investigated the amount of time a young and exceptional chess player, CS, had studied alone and engaged in other chess-related experiences. CS spent little time studying alone and little time engaging in other chess-related experiences. Nonetheless, she achieved an exceptional chess level. CS’s achievement is difficult to reconcile with Ericsson’s 10-year/10,000-hour practice rule. Study 2 investigated factors contributing to the chess skills of 77 adult chess subjects, showing that time spent studying alone and time spent engaging in other chess-related activities are strongly related to chess skill. However, contrary to the theory of deliberate practice and recognition-action theory, other factors including domain-general fluid intelligence, domain-specific fluid intelligence, and domain-specific crystallized intelligence all contributed to chess skill even after controlling for practice and other chess-related activities. These findings support the view that spending time studying alone and playing chess is necessary, but not sufficient to achieve a high chess performance level.