Recently, prognostics and health management (PHM) has emerged as a key enabling technology to overcome the limitations of traditional reliability analysis. Conventional reliability and maintenance frameworks rarely consider the actual individual health status of engineering systems while operating for operation and maintenance decision making. In engineering practice, we are often more interested in investigating the remaining useful life (RUL) of a specific unit under its actual use condition in order to determine the advent of a failure and prevent the failure from occurring. PHM focuses on utilizing performance signals acquired from an engineered system to monitor the health condition and predict the RUL of the system over its entire life cycle. This paper provides reviews of the general PHM framework for integrating state-of-the-art tools and techniques that can be used to automatically detect, diagnose, prognosis the effects of abnormal events in an engineered system on its ultimate performance and bridge future decision support. In some cases, it may become essential to assess in an automated fashion, the impact of the anomaly on overall system performance using an unified performance metrics. This relies on an estimate of the RUL based on prognostics of engineering system. Thus, by enabling such a framework, it can bring us more efficient planning and execution of maintenance to reduce life cycle costs and/or increase profits.