This catchword article presents the concept of “Inter-Cloud Computing” which introduces an additional management layer on top of conventional Cloud Computing Systems. Its goal is to reach a higher level of sustainability by autonomously shifting resources among the participating Cloud systems when unexpected load levels occur or disasters strike. Cloud systems are widely seen as a promising paradigm for an IT infrastructure that is capable of creating an added value for business, society, and administration. If Cloud systems are to be applied to critical areas, such as enterprises’ core businesses, governmental systems, medical applications, and other social infrastructure services, it is crucial to guarantee end-to-end service quality that covers the involved external networks, and to meet a set of requirements regarding reliability (including security), compliance, governance, and power efficiency. However, if services are provided by a single Cloud system – which is the usual case today – unexpected levels of overload traffic from the Internet or natural disasters may affect the system’s reliable functioning. The ability of a single Cloud to request reserved resources is usually fixed by limited bounds. Therefore, unexpected loads and failures can easily overburden a single Cloud system and lead to unreliable and interrupted services. In order to enable a Cloud system to continue the delivery of guaranteed service levels even in such cases, it is indispensable to introduce a super-ordinate layer of Cloud organization which manages multiple Cloud systems so that they complement each other. Thus single Cloud systems, which are interconnected via broadband networks, can mutually request required resources from their peers, or provide available capacity to them, respectively. This flavor of Cloud Computing is called Inter-Cloud Computing.