An examination is made of 106 negotiated trades of at least 5% of the common stock of New York Stock Exchange (NYSE)- and American Stock Exchange (AMEX)-listed corporations. When a block trades and the firm is not acquired fully, cumulative abnormal returns average 5.6% and 33% of the chief executives are replaced within a year. Stock-price increases are larger when control passes to the new blockholder, when management does not resist the blockholder's effort to influence corporate policy, and when the block purchaser eventually fully acquires the firm. These findings indicate that the specific skills and expertise of blockholders - and not just the concentration of ownership - are important determinants of firm value. The modern public corporation is like any other asset in that its value depends in part on the skills of its owners.