Abstract Authors are associated with the Instrumentation System of Power Plants for over decades and are still in touch with modern technology. This book is the outcome of their experiences to benefit practicing engineers and students associated with power plants. Power Plant concepts are based on Laws of Thermodynamics depicting the relations among Heat, Work, property of system, Specific Weight / Volume, Path, Process, etc. Definitions of different types of Energy, Work, Boyle’s Law & Charles Law with general and combined equations, Avogadro’s Law / Hypothesis, Universal Gas Constant, Enthalpy, Entropy, Rankin and other cycles are touched upon in this Chapter along with Pressure – Volume and Temperature-Entropy Diagram for steam, different types of Boilers, Turbines, Condensers and Regenerative cycles. These recapitulations have been done at the beginning to enable reader to refresh basic knowledge on power plants.