This paper develops and applies the Essex Score approach to classifying life chances. This is in essence a class measure, insofar as it identifies the extent of access (of individuals and households) to those resources which determine the distribution of economic power within the society. However it consists, not of distinct categories, but of a continuous indication of human capital, constructed as a composite of education, recent work experience and occupational attainment. Its theoretical basis is straightforward; the mechanisms which connect these characteristics together, and which associate them with life-outcomes, can be simply and clearly specified. Its practical advantages include: its comprehensiveness of coverage across the population irrespective of past and present employment status; and its continuous measurement, which allows aggregation from individual to household levels of measurement, as well the sensitive investigation of the determinants and consequences of changes in social position during the life-course. The Essex Score is designed as a tool to investigate patterns of differentiation in life-chances. However the illustrative application that follows focuses more specifically on the study of social mobility. It brings together inter-generational and life-course processes in the UK into a single analysis, covering the influences of parents position, schooling, educational attainment, as well as the consequences of job performance and household or family formation processes. The Essex Score is calibrated from the British Household Panel Study, and the analyses of mobility processes are based on this same source. The work described here is part of the Social Position and Life Chances (SPLC) research project (described in Social Structure and Life Chances, ISER Working Paper 2001-20).