This chapter reviews the main models and concepts defined in IEC 61499 to gain a general overview of the function block standard. It is advisable to have some understanding of the material in this chapter before proceeding into any of the following chapters where specific features of IEC 61499 are reviewed in more detail. Topics covered in this chapter include: characteristics of function blocks and their execution; the different forms of function blocks; service interface function blocks to provide interfaces into hardware and operating systems; models to represent applications independent from the system configuration; the system, device and resource models for distributed control systems; the distribution model which assigns applications to the devices and resources; and exchange and storage formats for IEC 61499 entities.