An influential theory of chess skill holds that expertise in chess is not due to greater depth of search by experts but, rather, to the ability to recognize familiar patterns of pieces. Although there is evidence that experts search deeper than non-experts, the data are not consistent. In this thesis, I propose “key-position theory” which states that only in a small number of key positions is it necessary to search deeply and it is these positions that experts search deeper than non-experts. Study 1 found, consistent with key-position theory, that the distribution of moves times is extremely skewed with some moves taking much longer than others. This pattern was more pronounced for the stronger players. Study 2 found that the errors made by weaker players involved less search than the errors made by stronger players. These findings suggest that search is an important component of chess expertise.