This course is intended for those seeking a basic knowledge about window retrofit projects and the role they play in saving energyi n residential and commercial buildings. The course offers an introduction to how windows perform, common challenges facing retr ofit projects, and some options for meeting these challenges. The course provides a strong foundation of knowledge for homeowners, buildi ng managers, designers, and developers. The course also reviews a case study that explains how retrofitting the windows in the Empire State Building significantly reduced energy consumption while providing a return on investment in just five years.