Functional Safety is the part of the overall system safety which depends on the correct functioning of safety-related systems for risk reduction. The intended functions of these systems, i.e. the safety functions, must be executed under defined fault conditions with a defined 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) or IEC 62061 (Machinery) specify the requirements for various applications. Modern technical systems operating and controlling safety-critical processes are more and more complex because the requirements are increasingly multifaceted. This book discusses the monitoring or controlling of vehicles, railways and aircraft, machinery, power stations or chemical plants as well as medical equipment or systems in other safety-critical areas. Reliability means the functioning under all conditions. In modern systems in particular, the complexity of the software has increased to such an extent that faults can never be ruled out completely. In this context, safety means that the system will not assume a critical state, even if a fault occurs. This book examines the standards, reviews measures for determining risk and risk reduction, the different safety levels (SIL1 to SIL4), hardware and software components as well as corresponding models, needed mathematical procedures, various safety systems and contains numerous examples of how these concepts have been applied in various sectors. As such, it offers valuable support for understanding and realising safe electrical, electronic and electronic programmable systems (E/E/PES).