Agreements, are contracts, letters of intent (LOI), memorandum of understanding (MOU), service level agreements (SLA), statements of work (SOW), email, written or verbal agreements. They are created as outputs from the conduct procurements and control procurements processes. Once created the agreements are inputs to the develop project charter, determine budget and control procurements. Internal agreements can be informal. Generally, the less close the relationship, the more formal the agreement. When contracts or other legal documentation is desired, legal review may need to be added to the project plan and costs. The legal reviewers may be added to the stakeholder register.
See section 18.104.22.168 of the PMBOK 5th edition.