The objective of our research is to define a requirements model for Adaptive Multi-organizational Systems. Our work considers the functional complexity of contemporary internet-based, multi-organizational systems. Not only the business functions, but also the interactions between the components of such systems are highly dynamic and global. Furthermore, these systems function in extremely uncertain environments. This contextual uncertainty demands adaptability which further complicates the task of requirements modeling. Our model addresses this complexity by using a hierarchy of artifacts: goals encapsulating tasks, roles encapsulating goals, and organizations encapsulating roles. We express adaptation requirements in terms of non-functional requirements, quality constraints, and domain assumptions. Adaptivity is then modeled in all three organizational layers: goals, roles, and organizations. Contrary to existing methods, our approach enables modeling adaptivity and reduces the requirements modeling complexity in Adaptive Multi-organizational Systems.