Psychologists and philosophers tend to treat expertise as a property of special individuals. These are individuals who have devoted much more time than the general population to the acquisition of their specific expertises. They are often said to pass through stages as they move toward becoming experts, for example, passing from an early stage, in which they follow self-conscious rules, to an expert stage in which skills are executed unconsciously. This approach is ‘one-dimensional’. Here, two extra dimensions are added. They are drawn from the programme known as Studies of Expertise and Experience (SEE) and its ‘Periodic Table of Expertises’. SEE, which is sociological, and/or Wittgensteinian, in inspiration, takes expertise to be the property of groups; there are ‘domains’ of expertise. Under SEE, level of expertise grows with embedding in the society of domain experts; the key is the transmission of domain-specific tacit knowledge. Thus, one extra dimension is degree of exposure to tacit knowledge. Under SEE, domains can be big or small so there can be ‘ubiquitous tacit knowledge’, such as natural-language-speaking or other elements of general social behaviour, which belong to every member of a society. The second extra dimension is, therefore, ‘esotericity’. The resulting three-dimensional ‘expertise-space’ can be explored in a number of ways which reveal the narrowness of the analysis and the mistakes that have been made under the one-dimensional model.