Building upon the current emphasis on the importance of assets in increasing the productivity and reducing the vulnerability of poor peoples' livelihoods, a conceptual framework is developed that relates the functions and attributes of poor peoples' assets to their livelihood status and strategies. The framework promotes more integrated consideration of different assets held by the poor, and hence facilitates analysis for policy, capacity building and technological interventions to expand livelihood opportunities for the poor. The application of the conceptual framework is illustrated with preliminary analysis of small livestock keeping by campesinos in south east Mexico.