The population of ruminant livestock in Indonesia, increased during the past ten years, at an annual rate of 6.73% (beef cattle), 18.58% (dairy cattle), 5.07% (sheep) and 4.84% (goats). Feed for ruminants was mainly obtained from native grasses/legume shrubs and tree leaves and, to a lesser extent, from crop by-products and residues. The use of concentrate feeds was still limited to dairy cows. Seasonal variations particularly regarding rainfall, pose a constraint on forage supply in most of the regions of the country. Technology for the improvement of the feeding systems has been based either on the improvement of the environmental capacity to produce forage throughout the year or on the improvement of the animal physiological capacity, which is mainly achieved by manipulating the digestive tract ecosystems. The three strata forage production system has been introduced to farmers to ensure the continuous year round forage availability. Rumen microbial fermentative control has also been a subject of interest in order to improve the efficiency of feed utilization. The future prospects of research in nutrition and physiology of ruminants will be very likely directed toward research on and application of treated crop byproducts and concentrate feeds produced by biotechnology.