Within Latin America, Uruguay stands out by its equalitarian income distribution, the solidity of its democratic institutions, and its level of social integration. Over the last decade, however, there have been signs of cracks in this desirable image which adversely affect the harmony of social relations. These cracks take the form of marginal behaviour: i.e., types of behaviour which are not governed by socially accepted patterns. In this study, the explanation for these types of behaviour has been sought in the divergences between cultural goals, the structures of opportunities for attaining those goals, and the shaping of individual capacities for taking advantage of them. A central premise of the approach adopted is that the factors determining marginal forms of behaviour build up their effects in a cyclical manner throughout the different stages of individual lives and from generation to generation. In view of this cyclical character, no decisions on the priorities to be followed in tackling situations of marginality can be fully effective unless an overall view is taken. Hence, the design of an integrated social policy that seeks to restore the links of marginal persons with society must, at the very least: i); assemble the fullest possible picture of situations of marginality in the course of a person's life; ii); identify, in each stage, the conditions that help to build up and consolidate marginality, and iii); identify points of intervention which, because of their cost-benefit ratios, are of crucial importance for breaking the links that make possible the individual accumulation and intergenerational reproduction of situations of marginality. The article highlights the differences between poverty and marginal poverty, not because it assumes that marginality is confined to the poor, but because it is in that sector that the forms of marginality of greatest individual and social cost are concentrated. It is suggested that the key element in this differentiation is social capital, the depletion of which is due mainly to the break-up of the family and to processes of segmentation such as housing segregation --the most extreme example of which is the shanty towns-- and deterioration of the integrative function of the educational system.