Abstract: A system for monitoring usage of cloud resources across multiple cloud services, comprising a unified data engine and a virtual tag engine. The unified data engine is adapted to collect cloud resources usage data relating to a plurality of cloud resources of a plurality of cloud services used by a plurality of clients, and update, based on the cloud resources usage data, a unified data structure mapping usage of the plurality of cloud resources by the plurality of clients. The virtual tag engine is adapted to generate one or more virtual tags based on one or more tag rules for monitoring usage of one or more cloud resources of multiple cloud services by one or more of the plurality of clients, apply the virtual tag(s) to the unified data structure, and execute one or more multi-cloud operations over the multiple cloud services using the virtual tag(s).