An agreement among stockholders, typically in a private company, to ensure maintenance of stable ownership and management of a company for the life of the investment. Venture capital investors will typically require a stockholder agreement that may cover, among other things: a right of first refusal in favour of the issuer or other stockholders on a proposed sale by a stockholder of his or her stock, a right to participate in insider sales (i.e. sales by existing shareholders); an agreement to elect certain directors; and provisions as to buyout.