The EUREC4A-OA expedition of the RV L’ATALANTE was a contribution to the international research initiative EUREC4A (www.eurec4a.eu) and to the ocean-atmosphere related JPI project EUREC4A-OA. The cruise was carried out in concert with the Germans MSM89 on board of the RV MARIA S MERIAN and M161 campaign on the RV METEOR. Airplanes and drone operations as well as well as continuous observations from the ground-based site on the Island of Barbados (BCO) were part of the large EUREC4A experiment and they were taking place in parallel to the EUREC4A-OA cruise. Moreover, the cruise was coordinated with ships and Saildrones© operations in the context of the US American ATOMIC project. The overall goal of the EUREC4A field campaign was to collect observational data that will enable research on dynamic and thermodynamic processes in the atmosphere and ocean that will bring the understanding of the role of clouds, of nonlinear ocean dynamics and its interactions with the atmosphere in the climate system to a new level. The L’ATALANTE EUREC4A-OA cruise had its focus on the ocean/atmosphere coupling across ocean mesoscale eddies and submesoscale filaments. For this purpose, both ocean and atmosphere profile measurements were carried out to observe the temporal evolution and spatial heterogeneity of the atmospheric and oceanic boundary layer. Autonomous observing platforms (underwater gliders) and ship towed platform (Cloudkites on the German ships) augmented the ship-based observations. Two automated observing systems of the ocean-atmosphere interface, OCARINA and PICCOLO were also deployed for the first time in the open ocean and showed their performance and importance.