This book focuses on the use of Event-B as a formal method for software modelling and verification. Our case study is the elevator control system (ECS). Elevator Requirements are translated into mathematical Event-B models. We use RODIN to develop, test and verify ECS Event-B models before we can implement the system into a Software program. Event-B modeling is so vital that we can identify missing requirements, errors in our design and proof that the system model will function as expected than if we develop a system immediately after receiving requirements from the client. These requirements are incomplete and ambiguous. With the use of Event-B, we reduce the cost of system development since errors will always be discovered in the early stages of development. Transition from the requirements phase to formal specification phase is one of the most challenging steps. In fact, building initial models from system requirements requires a high level of competence and practical skills in Event-B Modelling.Since there is no well-defined process to guide system Engineers, this book provides a practical approach on how to develop good software systems.