Abstract. Workflows are operational business processes. Workfow Management Systems (WFMS) are concerned with the control and coordination of these workflows. In recent years, there has been a trend to integrate WFMS in distributed inter-organizational systems. In this case malfunctioning of one WFMS can affect more than one organization, making the correct functioning of a WFMS a critical issue. Thus, an important function of WFMS is to enforce the security of these interorganizational workflows. Several works have been done to integrate the security aspects in the workflow specification. Unfortunately, these research works generally adopt a centralized management approach and are based on static access control models. Therefore, they do not deal with flow control, a very important requirement in WFMS. In this paper, we suggest a decentralized and dynamic approach to handle a security policy in workflows taking into account access and flow control.