The American Association of Variable Star Observers (AAVSO) is a non-profit organization dedicated to the study of variable stars. Founded in 1911, it encourages amateur and professional astronomers to observe and report changes in brightness of these stars, contributing valuable data to the scientific community. AAVSO provides resources, training, and tools for observers, including a database of variable star information and software for data analysis. The organization plays a crucial role in advancing our understanding of stellar behavior and supports various research projects in collaboration with institutions worldwide.