This conference paper is based on Standard 90.1 to provide several selected energy efficiency measures (EEMs) in existing buildings for energy efficient operation and management. The examples of the EEMs are presented to explain the convergence of Standard 90.1, 62.1 and 55 – to provide acceptable indoor air quality and thermal environmental conditions for human occupancy while optimizing energy efficiency in built environment. These concepts of the EEMs can be also applied to new construction and major renovation.