Dynamic inter-organizational business process management (DIBPM) combines service-oriented business integration (SOBI) and work ow management as a promising approach for supporting commercial businessto- business (B2B) activities over web-based infrastructures. SOBI applies concepts from the eld of serviceoriented computing in the domain of dynamic business collaboration. Currently, SOBI technologies insuf ciently support B2B collaboration where dynamic matching of structures of service consuming and service providing processes is performed. Collaborating parties want to control how much process detail they expose and which parts of them are monitorable. SOBI technology should offer rigor that permits veri cation of desirable features before enactment, e.g., correct termination. Furthermore, current SOBI technologies lack concepts which are useful for specifying and implementing B2B collaborations. Hence, several related critical issues are explored in this paper. Firstly, how to manage the inherent conceptual, business, and technological complexity of such business collaboration. Secondly, the issue is addressed of laying a foundation for rigor that is instrumental for verifying control- ow adherence and correct termination of coupled business processes. These requirements need to be guiding for the development of speci cation languages of inter-organizational business processes and related middleware that enact them in a web-based way. Exploring these critical issues leads to the proposal of Sourcing that employs a three-level framework for tackling the complexity of dynamically matching a service consuming and a service providing process. Furthermore, Sourcing offers rigor by utilizing well explored process theory that results in improved control over inter-organizational business process structure. Finally, the issue of suitability is tackled by discovering inherent Sourcing features that permit the positioning of Sourcing con gurations in differing perspectives. Those values are instrumental for subsequently discovering patterns that are translatable into a language for full- edged DIBPM support.