Soils representing six great groups were collected from 11 states and Puerto Rico. These soils were selected to provide a broad range in characteristics normally associated with phosphorus adsorption. Regression analysis indicated that aluminum and organic matter in the soil are primarily responsible for phosphorus adsorption. The pH 4.8 NH4OAc extractable aluminum and HCl-NaOH extractable aluminum were particularly useful in accounting for phosphorus adsorption. From the data obtained, it appears that iron probably occupies a secondary role in phosphorus adsorption by soil, becoming important only in local regions where aluminum and/or organic matter content is relatively constant.