This presentation will summarize the last forty-five years of indoor air quality (IAQ) studies, investigations and research from the first energy crisis in the USA in the 1970’s to the latest issues with regards to climate change and its effect on IAQ. The initial occupant complaints about the quality of the air in buildings coincided with changes in infiltration and ventilation in buildings. In particular, the first ASHRAE 62 Standard was issued in 1973, and then substantially changed in the 1981 version. Subsequent versions of the ASHRAE 62 Standard have varied the ventilation flow rate that is acceptable for acceptable indoor air quality. The latest version (62.1-2016) will also be discussed in detail.