The neotropical savannas (243 million hectares) in South America are one of the most rapidly expanding agricultural frontiers in the world. Lessons from the experience in the Brazilian Cerrados suggest that crop and pasture monocultures are not sustainable under the current management practices. The challenge to achieve sustainable crop and livestock production systems is to generate technologies that can maintain high levels of productivity, while minimizing environmental risks. To achieve this it is necessary to overcome soil physical, chemical and biological limitations and to fight against soil degradation when subjected to monocropping, even under high-level of fertilizer applications. These processes are not well documented yet. A comparative analysis of major soil constraints for crop-livestock production in the Llanos with the soil quality needed for sustainable productivity, lead to the conclusion that these soils must be improved in terms of physical, chemical and biological conditions to make them productive and to move them to conservation agriculture (no-tillage) systems. This statement is supported by the results of two long-term experiments. To improve soils, experiments were established and from them the concept of building up an arable layer was developed. The arable layer concept proposed is based on combining: (1) adapted crop and forage germplasm; (2) vertical tillage to overcome soil physical constraints; (3) use of chemical amendments to enhance soil fertility; and (4) use of agropastoral systems to improve rooting and soil quality. No-tillage, minimum tillage, and integrated crop/livestock systems are proving successful technologies in terms of farmer adoption. However, to ensure that, over the long term, these marginal savanna lands are being developed in a sustainable manner, we need to understand the principles and functioning of these systems; appreciate the social, cultural, and economic aspects involved; promote a favorable policy environment; and seek an improved understanding of sustainability and its measurement.