Matrix teams generally occur in organizations that are run along project lines. The organization typically has to deliver a number of projects to achieve its objectives. Each project has a project manager, but the project team members are drawn from functional areas of the organization. Often projects are clustered together to form programmes, or indeed whole divisions or business units (for example, aerospace, defence or oil industry projects). Thus the team members have accountability both to the project manager and to their functional head. The balance of power between the projects and the functions varies from organization to organization, and the success of such structures often depends on the degree to which the project teams are enabled by the structure and the degree to which they are disabled.