Recently, organizations have shown more interest in cloud computing because of the many advantages they provide (cost savings, storage capacity, scalability, and speed of loading). Enterprise resource planning (ERP) systems are one of the most important systems that have been upgraded to cloud computing. In this thesis, we focus on cloud ERP interoperability, which is an important challenge in cloud ERP. Interoperability is the ability of different components to work in independent clouds with no or minimum user effort. More than 20% of the risk rate of cloud adoption is caused by interoperability. Thus, we propose web services as a solution for cloud ERP interoperability. The proposed solution increases interoperability between different cloud service providers and between cloud ERP systems with other applications in a company. .