The science of extrasolar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of groundbased surveys and dedicated space missions has resulted in 800-plus planets being detected, and over 2000 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earthlike planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are? The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of transiting exoplanets over the widest range possible. In the frame of ESA's Cosmic Vision programme, the Exoplanet Characterisation Observatory (EChO) has been considered as medium- sized M3 mission candidate for launch in the 2022 - 2024 timeframe [3]. The current 'Phase-A study' space-mission concept is a 1.2 metre class telescope, passively cooled to ~50 K and orbiting around the second Lagrangian Point (L2). The current baseline for the payload consists of four integrated spectrographs providing continuous spectral coverage from 0.5 - 16mum at resolution ranging from R ~ 300 to 30.