The term “policy” can mean many different things to people depending on the context, background, and application domain. This chapter provided a formal definition of “policy” in the system management context, and discussed different types of practical policies and their usages. In particular, it singled out configuration constraint policy, metric constraint policy, action policy, and alert policy. It then briefly introduced that they can be represented in a policy information model in the form of condition-action rules or event-condition-action rules. We will review the policy information model more in detail in Chapter 3. The chapter also presented high-level scenarios for using policies for self-management of a system. The characteristics of self management have been studied in the context of self-configuration, self-optimization, self-healing, and self-protection. Finally, the chapter described a generic architecture for policy-based management systems as defined by IETF and DMTF. More specific examples of policy-based management systems will be presented in later chapters.