The ability to effectively conceptualize services plays a key role in service design. Yet, action-relevant insights for service designers on how this crucial phase of service design could be systematically pursued remain surprisingly limited. This paper explores "modular reuse", a frequently used principle to efficiently implement and modify service processes in downstream, i.e. implementation, activities as a possible underlying mechanism to inspire and facilitate the conceptualization phase. In a Design Science Research approach, we develop and formatively evaluate three design principles, which enable the purposeful reuse of existing service elements for the conceptualization of new services. This research contributes by 1) tapping into novel ways to improve the conceptualization phase of service design, proposing an underlying mechanism to increase its effectiveness; 2) providing initial design principles that serve as prescriptive guidelines in the creation of new methods and tools to leverage the idea of modular reuse for the conceptualization of new services.