 The Atmospheric Correction Intercomparison Exercise, ACIX, is an international initiative designed to compare the performance of different atmospheric correction algorithms. Twelve teams participated in the exercise by applying their algorithms to Landsat 8 and Sentinel 2 images from various locations around the world. The results showed that each team's approach had its own strengths and weaknesses, highlighting the need for further algorithm development. This article was authored by Georgia Doxonee, Eric Vermote, Jean-Claude Roger, and others.