THE POSTWAR PERIOD has seen an almost unbelievable expansion of residential housing, a growth which confounded many prophets, and which went a long way toward underwriting the high level of prosperity. Even now the magnitude of this boom has not yet been fully recognized. Mortgage debt on oneto four-family non-farm homes more than doubled in the five-year period immediately following World War II, increasing from less than $20 billion at year-end I945 to almost $47 billion at year-end I950. In I950 alone the increase totaled $7.8 billion-more than the total increase in loans and investments of all active banks in the United States during the same period. In physical terms the boom has been equally impressive. The 4.9 million units started from I946 through I950 exceeds the total number of starts throughout the preceding fifteen years. The number of housing starts in I949 and in I950 exceeded those of any other year on record. At the present time (September, I951) the indications are that I95I will be the third consecutive million-house year. In the Defense Production Act of I950, Congress recognized the tremendous inflationary potential in home building. The Federal Reserve System, in concurrence with the Administrator of the Housing and Home Finance Agency, was charged with the responsibility for regulation of real estate financing. Despite these credit restrictions, which were widely denounced as overly restrictive, housing starts for the first half of I95I were the second highest on record. Although starts in July and August, the latest available as this article is written, were running at a lower level, it was evident that I95I would go down as one of the big years in home construction. Because of the continuing importance of residential construction, it may be well to look at salient characteristics of the lenders who furnished the funds for the most spectacular housing boom on record. Of the total increase of $2 7,288 million in mortgage debt on oneto four-family non-farm homes from year-end I945 through I950 (an increase in mortgage debt of I39 per cent), almost a third found its way into portfolios of savings and loan associations, which increased their holdings by $8,349 million to a total of $I3,725 million.