What is IaaS? Infrastructure as a service. How it is different from existing services in Windows Azure like Software as Service and Platform as Service? Saas and PaaS are service models where you can use the capabilities of Cloud computing to deliver services. Many customers adapting IaaS model because they have the capabilities for managing their software but not underlining physical infrastructure. if you adapt the Infrastructure as a service model from cloud computing then you no need to worry about infrastructure, storage and capacity. The main difference between Saas and IaaS is where installing software , updating patches etc need to do your self in IaaS. In SaaS it is the part of their service patching server, network maintenance and storage.