Abstract The authors have been associated with the Instrumentation Systems of Power Plants for more than two 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 the laws of thermodynamics depicting the relations among heat, work, properties of a system, specific weight/volume, path, process, etc. The definitions of different types of energy, work, Boyle's Law and Charles Law with general and combined equations, Avogadro's Law/Hypothesis, the universal gas constant, enthalpy, entropy, and Rankine and other cycles are touched upon in this chapter along with pressure-volume and temperature-entropy diagrams for steam as well as different types of boilers, turbines, condensers, and regenerative cycles. These recapitulations have been done at the beginning to enable the readers to refresh their basic knowledge on power plants.