This course explores how recent, significant changes to energy codes and standards are transforming the way commercial window systems are manufactured and specified. Key performance requirements - including Federal mandates and rating system upgrades − will be discussed, together with the specific performance criteria that new fenestration systems will need to meet. The importance of optimizing "whole window" performance − glazing, spacers, and framing − will be addressed, and a list of recent advances in window system design and construction will be reviewed. The course ends with a discussion of how the new energy requirements are changing the way commercial windows are specified; in particular, how specs need to combine elements from both the National Fenestration Rating Council and the American Architectural Manufacturing Association in order to be effective.