Indoor air quality (IAQ) refers to the attributes of indoor air that affects a person’s health. Despite there being many benefits for improving IAQ there isn't a universally accepted indicator parameter for monitoring IAQ. A systematic literature was undertaken to identify the literature exploring the potential for CO2 to be used as an indicator of indoor air quality. The relationships between different indoor air quality parameters and CO2 will be discussed as well as practical considerations. A case study will also be presented which investigated the effect of an evaporative cooling systems on CO2 levels in an indoor environment.