Looking back at Wall Street in the 1960's, historians of finance will almost certainly conclude that the decade's most important event was the "institutional transformation"--no simpler term seems available---of the stock market. When the 1960's began, pension funds, mutual funds, insurance companies and other institutions together held about 15 per cent of American-owned common stock. When the decade ended, institutions' shareholdings were up to about 25 per cent of the total; Manuel F. Cohen, the former chairman of the Securities and Exchange Commission, estimated the value of their holdings early this year at over $260 billion. In 1960, institutions accounted for less than 25 per cent of New York Stock Exchange volume. The figure now is over 40 per cent; in addition, a significant and rising amount of institutional trading now takes place off the board.