A mandatory corporate action is an event initiated by the board of directors of the corporation that affects all shareholders. Participation of shareholders is mandatory for these corporate actions. An example of a mandatory event would be a spin-off, where part of a company is spun-off to create a new company. If you have shares in the original company, you will receive shares of the new company whilst retaining your original investment. A voluntary corporate action is an action where the shareholders elect to participate in the action. A response is required for the corporation to process the action. A tender offer is an example of a voluntary event, where a third party wants to buy a portion of equity in your invested company, you will have the option to tender all or part of your investment. The event could eventually become a mandatory takeover where the third party attempts to buy the entire share capital leaving you without the choice to tender or not.