Résumé : Cross-organizational service-based processes are increasingly adopted by different companies when they can not achieve goals on their own. In order to guarantee that all involved partners are informed about errors that may happen in the collaboration, it is necessary to monitor the execution process by continuously observing and checking message exchanges during runtime. This allows a global process tracking and evaluation of process metrics. In this paper, we present an approach for decentralized monitoring of cross-organizational choreographies. We introduce the concept of External Flow Monitoring and define a hierarchical propagation model for exchanging external notifications between the collaborating parties. We also introduce the concept of EFM-view which allows partners to track the state of the choreography beyond their own processes. The collected monitoring data can be further used for the evaluation of global process metrics by expressing and evaluating statistical queries over execution traces.