Throughout the International Union of Geodesy and Geophysics's (IUGG's) centennial anniversary, the International Association of Geomagnetism and Aeronomy is holding a series of activities to underline the ground-breaking facts in the area of geomagnetism and aeronomy. Over 100 years, the history of these research fields is rich, and here we present a short tour through some of the International Association of Geomagnetism and Aeronomy's (IAGA's) major achievements. Starting with the scientific landscape before IAGA, through its foundation until the present, we review the research and achievements considering its complexity and variability, from geodynamo up to the Sun and outer space. While a number of the achievements were accomplished with direct IAGA involvement, the others represent the most important benchmarks of geomagnetism and aeronomy studies. In summary, IAGA is an important and active association with a long and rich history and prospective future.