In 2019, Colorado enacted House Bill 19-1261, establishing statewide greenhouse gas (GHG) emissions reduction goals. Colorado also enacted Senate Bill 19-096, requiring the Air Quality Control Commission (AQCC) within the Colorado Department of Public Health and Environment (CDPHE) to promulgate rules to collect and report on GHG data and to implement measures to meet these GHG emissions reduction goals. This issue brief provides an overview of AQCC rule making related to these legislative directives.