Performability of a product, a system or a service has been defined by this author (Misra in Inaugural Editorial of International Journal of Performability Engineering 1:1–3, 2005 [1] and Misra in Handbook of performability engineering, Springer, London, 2008 [2]) as an attribute of the holistic performance reckoned over its entire life cycle ensuring not only high dependability (quality, reliability, maintainability and safety) but also sustainability. Sustainability is a characteristic specific to a product, system or service. At the same time, a dependable product, system or service may not be sustainable. It may also be necessary here to point out that without dependability, sustainability is meaningless. Therefore, both dependability as well as sustainability attributes should be considered and must be evaluated in order to evaluate performability of a product. All other attributes of the definition of performability have been defined and can be computed except sustainability. In order to evaluate performability, it is therefore essential to define and compute sustainability. For developing sustainable products, systems and services in the twenty-first century, it is essential that we should be able to define precisely and quantify sustainability since one cannot improve what cannot be measured or assessed. The objective of the present chapter is to understand the implications of sustainability in order to facilitate computation of sustainability and thereby the performability. The purpose of 13 chapters in the Handbook (Misra in Handbook of performability engineering, Springer, London, 2008 [2]) by the author was to provide detailed introduction to each constituent elements of the definition of performability, namely quality, reliability, maintainability, safety and sustainability, and these chapters were received very well by the international academic community as is evident from Table 1.1. This was done with the intent to evoke interest among researchers across the world in the concept of performability leading to a way to compute or assess performability. But this did not happen in the past 12 years after the publication of the Handbook in 2008. The main impediment in this effort is the procedure to evaluate sustainability.