This report describes the outstanding floods in the United States during 1966. The four most destructive floods occurred during March-April in the Red River of the North basin in northwestern Minnesota, during April-May in northeastern Texas, in August, in east-central Nebraska, and in December, in the Southwestern United States. For the second consecutive year, there was severe flooding in the Red River of the North basin in Minnesota during ,the spring snowmelt period. Unseasonally warm temperature caused rapid melting of a heavy snow cover, with water equivalent ranging from 5 to 7 inches, which covered .the northern two-thirds of the basin. Peak discharges were maximum of record at three gaging sites having periods of record ranging from 20 to 30 years, ,and peak discharges exceeded 50-year floods at nine sites. Damage from the flood was estimated at $10 million. In the period April 22-29, from 20 to 26 inches of rain fell in parts of the Sabine River basin in northeastern Texas. and high rates of runoff occurred from the headwaters of the Sulphur River southward .to the Trinity River basin. Flood damage was estimated at $12 million, and at least 25 persons lost their lives. Severe floods occurred along the Loup River ,and its tributaries in east-central Nebraska on August 12-14. The .peak discharge at nearly all gaging stations in the flood area exceeded the previous maximum of record. The floods we re caused by heavy rains of from 13 to 17 inches in about 24 hours. The storm was the most widespread in the area since 1896 and may have exceeded the area of the 1896 storm. The floods were unusual because of the consistently high discharges throughout a large flood area. Flood damage was estimated at $11 million. In early December a storm moved eastward from the Pacific coast in southern California into Southwestern United States. Intense precipitation occurred around the mountain ranges of south-central California and in and extending from southeastern Nevada across the southwestern corner of Utah to the Grand Canyon and southward to the mountains of central Arizona. Discharges on many streams exceeded the previous maximums known, and the flood was particularly damaging because of the large area involved. In .addition to these four floods, 19 others of lesser magnitude are considered important enough to be included in this annual summary.