This chapter identifies and discusses the main properties of a Cloud environment. These are adaptability, scalability, resilience, availability, reliability, security, and privacy. Such properties are vital when comparing different Cloud providers. They are also important for Cloud providers when assessing their infrastructure and for introducing different business models. Importantly, Cloud properties provide measures which help in quantifying Cloud trustworthiness. Assessing the level of trust of a Cloud provider is one of the hot research topics in this area. A foundation of this is quantifying the Cloud properties. This chapter defines and discusses these properties; however, quantifying these properties is not an easy task and lots of work still needs to be done in this domain.
There are, of course, many definitions of the word ‘trust.’ For example, Diego Gambetta  defines trust as follows:
There are also a number of techniques that enable one party to establish trust with an unknown entity: direct interaction, trust negotiation, reputation, and trust recommendation and propagation. ...