Functional safety is the part of the overall system safety that depends on the correct functioning of safety-related systems for risk reduction. The intended functions of these systems, known as safety functions, must be executed under defined fault conditions with a high probability. For the first time, a standard, the relevant generic standard IEC 61508, demands a quantitative proof for the residual risk. The standards IEC 61511 (Process Industry), IEC 61513 (Nuclear Power Plants), and IEC 62061 (Machinery) specify the requirements for various applications. Modern technical systems that operate and control safety-critical processes are becoming increasingly complex due to multifaceted requirements. This book discusses the monitoring or controlling of vehicles, railways, aircraft, machinery, power stations, chemical plants, and medical equipment or systems.