URING January, 1937, a standing high-pressure area in the southwestern North Atlantic sent steamy tropical air into the United States day after day, which, on meeting a persistent flow of polar air in a nearly stationary southwest-northeast belt, precipitated phenomenal rainfalls. Locally exceeding 20 inches, the rains extended across the lower Mississippi and almost simultaneously over the entire Ohio basin. Dammed by the flooded lower Mississippi, the Ohio River became a lake, I5 miles wide in some places, and nearly Io feet above the highest stages previously known. All the river cities, except Cairo, were partially submerged; one sixth of Cincinnati was under water, one half of Evansville, two thirds or more of Louisville. This flood will probably be best known as the Louisville flood, since the inundation of this populous city drowned several persons and caused an estimated monetary loss of $200,000,000: that the loss of life was not very much greater was owing to the extraordinary service of the local radio station WHAS. In five days this station broadcast I6,500 separate appeals for help. The calls were heard on sound trucks at the shore and on radio-equipped boats that were thus able to effect the removal of at least 58,ooo persons from their flooded homes. The January rainfall at Louisville was I9.I inches, of which 10.14 fell in the five-day period January 20-25. The death toll for the whole flood is, at last reports, 436, the number of refugees 8oo,ooo to 970,ooo, and the monetary losses from $550,000,000 to well over $600,000,000. The value of some 300,000,000 tons of top soil that the Soil Conservation Service estimates has been carried away from the Ohio watershed is not included. The flood of I937 must be considered the greatest American flood on record. This unprecedented flood on the Ohio and lower Mississippi Rivers, coming so soon after the extraordinary floods of March-April, 1936, in the middle and north Atlantic states, compels an examination of the relation of floods to weather in an effort to solve or mitigate their menace. What are the meteorological features of previous great floods, such as those of I913, 1922, and 1927 in the Mississippi basin? of still earlier general floods, such as those of I882, I889, 1903? of the less widespread but remarkable overflows that followed excessive rains in July 1935, November 1927, July I9I6, and June I9I5? What flood control measures do meteorological considerations most favor? And are flooding rains predictable?