This chapter describes the available technologies for removing phosphorus and nitrogen from municipal sewage, with emphasis on those that are expected to see prominent use either because of their treatment capabilities or their ease and cost of operation, or both. The information is presented in two sequential blocks: one on the chemical, biological, and physical principles behind the available treatment technologies; a second on the design and operation of processes and systems based on these principles. Twenty percent of the total US treatment capacity is expected to be capable of removing phosphorus in the year 2000, a percentage that is twice as great as in 1982. As the approach of removing phosphorus from municipal wastewaters to control nuisance aquatic plant growth enters its third decade of application in the United States, two significant trends can be observed. Nitrogen removal is being considered on a broad-scale basis to reduce the availability of this nutrient to aquatic plants.