Most agricultural regions of California enjoy long growing seasons, fertile soils and irrigantion, all conditions that favor a highly diversified cropping. In addition, the wide variety of vegetables, field and tree crops determined a high diversity and flexibility of agricultural enterprises. Despite these factors, Californian agroecosystems are dominated by monocultural cropping systems. Although productive, these systems lack the ecological features to ensure efficient nutrient cycling, water and soil conservation, and biotic regulation. Productivity is subsidized with chemical inputs such as pesticides and fertilizers, some of which caue undesirable environmental and public health hazards. Large-scale monocultures are also highly susceptible to wind erosion and are dependent on ground water for irrigation, leading in some areas to a considerable ‘ leading in some areas to a considerable ‘overdraft’. In other regions, poor field drainage and rising water are leading to unacceptable soil salinity levels. In summary, Californian agriculture is very productive, but the environmental costs of such productivity is threatening the sustainability of agriculture. The search for self-sustaining, low-input, diversified and energy-efficient agricultural systems is now a major concern of researchers, farmers, policy makers and the public in California. The long tradition in biological pest control in California, as well as the experience of a number of organic farmers who developed low-input systems through ‘trial and error’, provide the building blocks for the search for a more sustainable agriculture. A key strategy is sustainable agriculture is to restore the agricultural diversity of the agricultural landscape. Diversity can be enhanced in lime through crop rotations and sequences, and in space in the form of cover crops, intercropping, agroforestry crop/livestock,mixturee, etc. Vegetation diversification not only results in pest regulation through restoration of natural controls, but also produces optimal nutrient recycling, energy conservation and less dependence on cultural inputs. In California although this new approach to agriculture is actively researched. realistically it will work only if it is economicically sensible and can be carried out within the constraints of a fairty normal agricultural system. Therefore, adoption of recommended diversification designs will procesd as these reduce costs and increase the efficiency and viability of farmers.