A shareholders' agreement (sometimes referred to in the U.S. as a stockholders' agreement) is an agreement between the shareholders of a company.

In strict legal theory, the relationships between the shareholders (as between themselves) and between the shareholders and the company are regulated by the constitutional documents of the company. However, where there are a relatively small number of shareholders it is quite common in practice for the shareholder to supplement the constitutional document There are a number of reasons why the shareholders must wish to supplement (or supersede) the constitutional documents of the company in this way:

• a company's constitutional documents are normally available for public inspection, whereas the terms of a shareholders' agreement, as a private law contract, are normally confidential between the parties.
• contractual arrangements are generally cheaper and less formal to form, administer, revise or terminate.
• the shareholders might wish to provide for disputes to be resolved by arbitration, or in the courts of a foreign country (meaning a country other than the country in which the company is incorporated). In some countries, corporate law does not permit such dispute resolution clauses to be included in the constitutional documents.
• greater flexibility; the shareholders may anticipate that the company's business requires regular changes to their arrangements, and it may be unwieldy to repeatedly amend the corporate constitution.
• corporate law in the relevant company may not provide sufficient protection for minority shareholders, who may seek to better protect their position by using a shareholders' agreement
• to provide mechanisms for removing minority shareholders which preserve the company as a going concern.