Aerosols, produced by both natural and anthropogenic processes, are integral in Earth’s climate system. They perturb the radiative budget and hydrologic cycle, through complicated interactions with clouds and the Earth’s surface. Understanding global aerosol distributions, variability and trends are a necessary step in understanding how the climate is changing. With its launch aboard Terra in late 1999, MODIS ushered in a new era of global aerosol monitoring. In particular, due to its extensive spectral range, wide viewing swath, and fine spatial resolution (1 km or better), MODIS may be capable of providing an accurate and dependable global aerosol optical depth (AOD) data set. My talk presents some highlights of what we have learned about remote sensing and global aerosols over the past nine years, as well as some of the unresolved issues that stand in the way of deriving the aerosol climate data record.