Phosphorus is generally recognized as a key nutrient in the fertility of fish ponds. This nutrient frequently limits plant production and ultimately influences fish production. Conversely, too much phosphorus is sometimes responsible for excessive production of blue-green algae or other nuisance plant species in ponds. Since phosphorus is extremely important in pond management schemes, an understanding of its physiochemical and biological dynamics is valuable to fishery biologists. This report is a description of phosphorus relationships in ponds. The discussion is a general consideration of the phosphorus cycle rather than an exhaustive review. No attempt was made to summarize data on correlations between phosphorus fertilization and fish production.