Controlling emissions from the in-use fleet, particularly from high emitters and older vehicles, can immediately alleviate urban air pollution. As pressure to address China's air quality issues builds, Guangdong Province has taken several steps toward that end. Cities in Guangdong have established programs based on their specific capabilities and needs. The most common include measures to identify high emitters, such as inspection and maintenance programs, remote sensing, spot-checking, public spotter initiatives; cleaner fuel programs; removing high emitters and older vehicles from the roads through scrappage programs as well as retrofit and repower programs; establishing low-emission zones; and vapor recovery at fueling stations, referred to as Stage II vapor recovery. This report summarizes best practices for these in-use control programs, and is intended to serve as guidelines for policymakers seeking to design, implement, and improve their programs at the local level. In addition, the report evaluates in-use vehicle emission control programs in four cities in Guangdong’s Pearl River Delta region: Guangzhou, Shenzhen, Foshan, and Dongguan.