The domain and facet approach to personality assessment is discussed. The strategy used to identify and measure aspects of the five factors of personality structure is described. Evidence concerning the factorial invariance of the resulting set of 30 facet scales and some recent evidence concerning their discriminant validity are reviewed. Some theoretical and practical applications of analysis on the level of facet scales are considered. When P. T. Costa and R. R. McCrae began to develop a measure of personality, they adopted a top-down approach to hierarchical assessment, resulting eventually in five domains (multifaceted collections of specific cognitive, affective, and behavioral tendencies), with the lower-level traits corresponding to these groupings known as facets. The pragmatic value of a facet-level approach to personality assessment is apparent. Individual facets contain a specific variance not represented in the global factors. The explicit measurement of facets also has implications for an understanding of the origins and nature of personality traits themselves, such as why traits co-vary along five dimensions. Six tables present information from various studies, and seven figures illustrate the relationships among the facets. (Contains 27 references.) (SLD)