46The idea behind cloud computing is to deliver Infrastructure-, Platform- and Software-as-a-Service (IaaS, PaaS and SaaS) over the Internet on an easy pay-per-use business model. However, current offerings from cloud providers are based on proprietary technologies. As a consequence, consumers run into a risk of a vendor lock-in with little flexibility in moving their services to other providers. This can hinder the advancement of cloud computing to small- and medium-sized enterprises. In this chapter, we present our work in outlining the motivations and current trends of achieving interoperability, especially in the area of IaaS. More specifically, this work delivers a comprehensive taxonomy as a guideline for cloud providers to enable interoperability within their cloud infrastructures. Thus, this taxonomy discusses important topics of IaaS, such as access mechanism, virtual appliance, security, and service-level agreement.