A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. The versatility and prospect of automation is so important that it could bring radical development in almost every aspect. The immediate objective of this book is to study and test the applicability of PLC. In this book, knowledge on PLC is obtained and its applications in different sectors are discussed. Also different types of PLCs are specified and briefly discussed. Among them, a PLC Trainer PLC-100 and LOGO 230 RC have been studied and several projects and experiments are done with PLC Trainer PLC-100. A general description about some common features of PLC is introduced. To understand the necessity and application of PLC in industrial automation, a PLC based control system is applied in an automatic bottle filling station using LOGO 230 RC.