We　summarized　published　evidence　linking　indoor　carbon　dioxide　(CO2)　concentrations　with　cognitive　performance,　physiological　responses,　and　health　effects.　We　included　studies　where　CO2　was　used　as　a　proxy　of　ventilation,　an　indicator　of　emissions　from　humans　(bioeffluents),　and　an　independent　exposure　factor.　Poor　ventilation,　demonstrated　by　high　indoor　CO2,　related　to　increased　prevalence　of　sick　building　syndrome　symptoms　(SBS)　and　decreased　cognitive　performance.　Exposures　to　both　human　bioeffluents　and　pure　CO2　could　impair　cognitive　performance　at　typical　indoor　levels　of　CO2≤5,　000　ppm.　The　effects　could　occur　at　different　CO2　levels,　depending　on　the　type　of　cognitive　task.　A　clear　physiological　explanation　of　the　observed　effects　requires　additional　research.　©　2022　17th　International　Conference　on　Indoor　Air　Quality　and　Climate,　INDOOR　AIR　2022.　All　rights　reserved.