This chapter focuses on the UEFI services that apply to the implementation of UEFI drivers. This includes descriptions of those services, along with code examples, that demonstrate how a UEFI driver typically uses those services. The EDK II provides a number of library functions that simplify the use of UEFI services as well as UEFI driver improvements in maintainability, portability, readability, robustness, and size. Additional descriptions and code examples using EDK II library functions also appear where applicable.