Abstract: Long-term observations of aerosol optical properties are crucial for quantifying the aerosol radiative forcing and climate effects as well as examining the air quality and environmental health. Herein, a systematic review of the global Aerosol Robotic Network (AERONET) is presented, and its development and research achievements at the Beijing station are introduced; this station has recorded the longest observation time in China. Furthermore, the multitime scale variability of optical radiation products is analyzed using more than 20 years of observation data from the Beijing station. Additionally, the importance and urgency of long-term observations are discussed.