Our knowledge of planets other than the eight "classical" Solar System bodies is in its infancy. We are discovering thousands of planets orbiting stars other than our own, and yet we know little about their chemistry, formation and evolution. Planetary science therefore stands at the threshold of a revolution in our knowledge and understanding of our place in the Universe: just how special are the Earth and our Solar System? It is only by undertaking a comprehensive chemical survey of the exoplanet population that we can hope to answer these critical questions.

Little more than ten years ago, the detection of a signal from an exoplanetary atmosphere was still in the realm of science fiction. Pioneering results were then obtained through transit and direct imaging spectroscopy with Hubble, Spitzer and ground-based facilities, making it possible the detection of ionic, atomic and molecular species and of the planet's thermal structure. With the arrival of improved or dedicated instruments in the coming decade, planetary science will expand beyond the narrow boundaries of our Solar System to encompass our whole Galaxy.