This paper provides an overview of Colorado's efforts to reduce particulate emissions from light- and heavy-duty vehicles. As a result of the passage of Senate Bill 193, Colorado has enacted several programs to control diesel emissions. These programs include a roadside opacity enforcement program, a pilot light-duty inspection program, and a public education program. Colorado is in the process of setting up Emissions Technical Centers for purposes of supporting the diesel opacity enforcement program. Currently, they are developing light- and heavy-duty test procedures. Colorado is planning numerous diesel related activities in the future. They will be investigating the relation between opacity and mass emissions, in order to better define correlation between the two indicators. CDH also will be performing much more research into test cycles and will be investigating a light- and heavy-duty I/M program. Considerable amounts of data will be available by next fall.