The home and building automation (HBA) is a technological effort aiming to make houses and buildings more controllable, autonomous, and comfortable. An HBA system requires a large deployment of sensors and actuators to detect contextual information and then transfer control data to all building components. The KNX system offers the possibility for the manufacturers to choose between several transmission media, according to market requirements and specific habits. The KNX system specification covers all technical elements of the standard, ranging from the low-level device details and certification rules to testing and application descriptions. This chapter summarizes some distinctive characteristics of the KNX standard at the application level. Application modeling is the responsibility of various application specification groups of the KNX Association. In order to plan, design, and commission a KNX installation, a software tool is required to assist designers and electrical installers. For that reason, a manufacturer-independent configuration tool named engineering tool software (ETS) was developed by the KNX Association.