Technical Abstract: The performance of continuously mixed anaerobic digesters was evaluated in the laboratory for treating manure, food waste and their mixtures at 35 ± 2oC and a hydraulic retention time of 20 days. The first mixture was composed of 32% and 68%, and the second was composed of 48% and 52% food waste and dairy manure, respectively. The percentage was based on volatile solids (VS). The digesters treating manure and the two mixtures showed stable performance at an organic loading rate (OLR) of 4 gVS/L. However, the digester treating food waste was not stable even at an OLR of 2 gVS/L as indicated by high volatile fatty acid concentrations and low pH. The pH adjustment by adding hydrated lime to the food waste increased biogas production rate and yield. The microbial analysis results showed that the food waste derived library contained statistically greater numbers of clones related to the phyla Thermotogae and Actinobacteria and the manure derived library contained greater amounts of clones related to the phyla Firmicutes, Bacteriodetes and Spirochetes. The archaeal population structure had little difference in the digesters fed with different substrates and was composed of hydrogenotrophic, acetotrophyic, and methylotrophic methanogens. The results of this study showed that co-digestion of food waste and dairy manure could significantly increase the biogas production rate and therefore the economics of the digester system as compared to digestion of dairy manure alone. Adding food waste into dairy digesters would be a feasible method for improving the economics of dairy farm digesters.