Corporations retain the right to issue new shares of stock, which could dilute the ownership of existing stockholders. Existing shareholders often hold preemptive rights, which allow the shareholders to purchase these new shares of stock before they are made available to the public. Thus, if a shareholder owns 10 percent of a corporation, and the corporation issues new stock, the shareholder would own less than 10 percent if he or she did not purchase new stock. If the shareholder exercises preemptive rights, he or she may purchase as many new shares as necessary to retain that 10 percent interest.