Observatories of the climate system are essential to assess future climate predictions that are central and fundamental requirements for determining future mitigation strategies. such observing platforms are very few ones in the tropical southern hemisphere. Cnrs, Université de la réunion, région réunion and the european FeDer program support together the construction of a high- altitude observatory which is operational since October 2012 in La Réunion (South West Indian Ocean, 2160 m asl, latitude 21°S, longitude 55°E). The Maïdo observatory takes over from its predecessor programs at sea level over the island who started long-term observation data of atmospheric chemical composition since 1994. the Maïdo observatory is an ideal platform to sample the atmosphere with different techniques (in-situ analysers, radiosounding, passive and active remote sensing) and to record surface measurements and vertical profiles from ground to the mesosphere over a subtropical latitude band poorly sampled by other international programs. The Maïdo observatory hosts lidars, one UV spectrometer, one radiosonding station, Ftir spectrometers, microwave radiometers, one lightning antenna, cameras, one Gnss station, microbarometers, etc. these devices sample many atmospheric parameters (e.g., meteorological parameters, reactive and greenhouse gases, aerosols, lightning and transient luminous events, infrasounds, etc). part of this very extensive range of instruments is approved and belongs to international networks like nDaCC (network for the Detection of atmospheric Composition Change), sHaDOZ (southern Hemisphere aDditional OZonesondes), tCCOn (total Carbon Column Observing network), and WWLLN (World Wide Lightning Location Network). in-situ analysers regroup measurements of reactive and greenhouse gases, and aerosols measurements approved by or applying to networks like GAW/WMO (Global Atmospheric Watching / World Meteorological Organization), iCOs (integrated Carbon Observing system). The Maïdo observatory is currently the only way to provide regular remote and in-situ atmospheric observations at subtropical latitudes and at high resolutions (seconds in time, few tenths of meters vertically) over a marine-remote region poorly sampled by other programs. it provides data for users in science and policy including air quality forecasting, verification of CO2 emissions and Kyoto monitoring, numerical weather prediction, and validation of global chemical transport model, global climate chemical model and satellite products. since its participation in on-going european projects (nOrs, aCtris-2, arise-2), and thanks to the start of delivery of data in near real time, the Maïdo observatory will largely contribute to the Copernicus atmosphere Monitoring services (CaMs). the Maïdo observatory is open to transnational access thanks to its participation in european programmes like aCtris-2 and enVriplus. this presentation will give an overview of results achieved so far and a number of highlights to illustrate the promise Maïdo observatory data hold for the future, allowing new applications and analysis for a broad community of users.