(1) A total of 27 nests of the Tree Swallow were examined for nest structure, nesting materials, and animal remains. (2) Dimensions, weights, and location of the nest cup were recorded for 19 of these nests which were complete but unused. All 19 nests were taken apart and the nesting materials identified when possible. (3) The quantities of the various plant parts making up the nests varied indirectly with the distance to the nearest source of the species involved. Accessibility of the source modified this relationship. (4) Nesting materials were obtained from the ground. (5) Feathers were in every nest, most of them light colored, possibly serving to reflect light into the nest. (6) Many insects were in the nests, two of which (fleas and blowflies) were heavily parasitic on the swallows. (7) Shells of fresh water molluscs (having been fed to the young) were found in six of the eight nests that reared young.