e entity is a hardware or software element, cloud site, functional capability, application VF, etc. Both control plane (provisioning) and service data plane (VF reachability) availability need to be considered. Downtime in minutes/year is calculated as 525,600*(1-availability). Availability and downtime can be either unplanned (due to hardware failures, software faults, etc.) or planned (due to maintenance, upgrades, etc.). Reliability is defined as the conditional time-dependent probability that the entity is still operational at time t given that it was operational at time 0. Mean-time-between-failures (MTBF) is commonly used as a simple surrogate for reliability. Resiliency, as used in this discussion, is the abil- ity of application software to recover from certain types of failures and yet remain functional from the customer perspective to achieve the goals of availability. Both reliability and resiliency items addressed in this chapter are intended to focus on areas that will benefit and support application availability. In addition to these time-based metrics, transaction-based metrics are critical in providing the full reliability picture. Service reliability (Tortorella, 2005a,b) provides a framework to character- ize user-perceived system behavior by defining and measuring transactional defects (e.g., dropped transactions, lost sessions in progress, excessive delays, timeouts, etc.). Transactional defects fall into three categories: accessibility (can I initiate my transaction?), continuity (can I complete my transaction?), and fulfillment (does my transaction complete in a timely manner?). Transaction defects are typically tracked and reported in terms of defects per million (DPMs) transactions. While critical to understanding the complete picture, transaction-based service reliability met- rics (as well as performance metrics) are not addressed in this chapter. This chapter also does not address performability, the joint analysis of performance and reliability (Wirth, 1988), or concepts such as "blast