Insight into the structure of the labor market and its operations in terms of careers can be gained through analysis of occupational mobility patterns at a detailed category level. Methodology components used to extend previous methods of defining career fields as evinced in mobility patterns are: (1) mobility matrix creation; (2) mobility weighting of job characteristics data; (3) pairwise dissimilarities coefficient computations; (4) cluster analysis of dissimilarities data; and (5) cluster decomposition along principal dimensions. The standard hierarchical cluster analysis algorithm is amended to yield a variable-connectedness method. The Occupation Systems Theory is developed which provides the conceptual basis for what is seen in the occupational mobility structure. Results of an empirical analysis of 275 detailed 1970 Census occupations and 117 job characteristics variables appear to conform with the recently advanced "job family" method of occupational classification, and the various clusters underscore the importance of the techological orientation of jobs as an intervening mechanism in career formation. (Although this data is based on past Census figures, the structure of analysis could be applied to more recent figures.) (Author/NRB)