Service engagements arise commonly in business and scientific computing. A service engagement is characterized by autonomous parties coming together in a contractual arrangement to share resources or carry out tasks for one another. Recent work shows how to model service engagements in an interactive manner and at a high level. This work formalizes the atoms of a service engagement as commitments among the participants, to be created and manipulated as the engagement progresses. Further, it scopes the commitments of an engagement in a (virtual) organization, and specifies how the policies of the participants affect their interactions. This paper contributes design patterns for service engagements formulated in terms of roles, commitments, and allied concepts. Each pattern reflects a distinct element of a service engagement from a business perspective and highlights exactly where policies apply. This enables the perspicuous, reusable specification of service engagements.