In a joint-stock company, the share capital is made up of the total contributions of the shareholders. Shares may be subject to public trading, providing an incentive to investors, who are needed for further business development. In a private company, stock can be transferred to anyone the current shareholder chooses, and usually shares are transferred under the terms of a share purchase agreement. A public joint-stock company‘s shares can be freely traded on the open market through a stock exchange, and so the list of shareholders is not fixed and can be changed in a flexible manner.