Modern systems and devices  (electronic systems,  electronic devices and components, electrical and  mechanical systems) are made to operate under  a number of extreme environmental  and operating  conditions. The resulting stresses can affect the working-life of the components  and test  their endurance to the limit.  Failure of systems and devices can be categorized in  a number of ways  such that  major failures, minor failures, parametric failures, catastrophic failures  etc.

    Increasing  the  ability of  the components and the devices to sustain such stresses, such that they operate  for longer periods of time without failure is the goal of  reliability engineering.   However not all systems are required to operate in a fail-free manner  through their  life-time. Many systems can be repaired when they fail. This brings into the fore the concepts of maintainability, system availability,  time to repair etc.

      While ensuring the reliability of  systems and devices,  one has to work under a number of constraints. These constraints or cost-factors  take into account the resources that are  available,  economic benefits , profitability  of such an exercise  etc. Thus optimization techniques have to applied  while  designing  reliable systems.

   The concept of   "QUALITY"   is closely  linked to that of reliability.  Quality is a static concept because it deals with  how closely the product   adheres to the given specification  and customer requirements.  It does not consider the degradation of the systems and devices  over period of time due to various stresses.

    Testing and  testability are  other important issue than concerns reliability engineers.  Predicting the workability and life-time of a product  before it is shipped  has a tremendous economic value in reducing servicing costs, warranty commitments  and in keeping the good name of the company.  Thus in today's world of  cut-throat competition, reliability  engineering of paramount importance.