1. a specific causative factor or element or an entire process that results in change, particularly in the sense of improvement. In psychotherapy research, a change agent may be a component or process in therapy that results in improvement in the behavior or psychological adaptation of a patient or client.

2. an individual who instigates or implements change within a social unit or situation (e.g., a family or group) or within an organization by communicating to, managing, and encouraging others in the change.