To implement integrated weed management more effectively, the temporal and spatial distribution of weed populations in a field need to be determined. Weed species tend to be patchy and this influences the ability to calculate average weed densities when conducting a survey. This chapter reviews current and evolving practices for the scouting and mapping of weed populations both during and across growing seasons. It considers the use of scouts on the ground; UAVs with cameras flying over the fields; and advanced software and computer-based tools to detect, identify and record weed species. The use of regional and global scales to understand changes in the occurrence of herbicide-resistant or invasive weed populations is also discussed.