Stéphane Udry is an astronomer at the Geneva Observatory in Switzerland, whose current work is primarily the search for extra-solar planets. He and his team, in 2007, discovered a possibly terrestrial planet in the habitable zone of the Gliese 581 planetary system, approximately 20 light years away in the constellation Libra. He also led the observational team that discovered HD 85512 b, another most promisingly habitable exoplanet.

The Geneva Observatory is an astronomical observatory at Sauverny (CH) in the municipality of Versoix, Canton of Geneva, in Switzerland. It shares its buildings with the astronomy department of the École Polytechnique Fédérale de Lausanne. It has been active in discovering exoplanets, in stellar photometry, modelling stellar evolution, and has been involved in the European Space Agency's Hipparcos, INTEGRAL, Gaia, and Planck missions.