Fluorescent brightening agents or optical brightening agents or fluorescent whitening agents are dyes that absorb light in the ultraviolet and violet region of the electromagnetic spectrum, and re-emit light in the blue region.

This creates a whitening effect by making materials look less yellow and by increasing the overall amount of light reflected to the eye. The most common class of chemicals with this property are the stilbenes. These chemicals are commonly part of laundry detergents to replace FWA removed during washing and enhance the appearance of garments.