Whole-Building Energy Modeling (BEM) is a multipurpose tool for energy efficiency, supporting design, operations, codes and standards, and research. This session aims to cover the various aspects associated with BEM in a practical but comprehensible way from the perspective of a practitioner. Besides the basic principles of BEM, such as the heat transfer in building systems and common energy modeling tools, this seminar also schematically illustrates the benefits of BEM in the design and operation of buildings for better energy performance. For beginners with limited experience on BEM, how to accurately and elegantly model the building energy system and its various components such as the envelopes, internal heat gains, central plant, and air distribution system is introduced from the perspectives of both engineering physics and hands-on experience.