With a 6.5-meter diameter primary mirror in space and a wavelength coverage from the visible to the mid-infrared, the James Webb Space Telescope (JWST) will soon open new windows to scrutinize transiting exoplanets' atmospheres. It will provide missing clues to understand hot Jupiter's atmospheres such as the relative abundances of molecular species and the thermal structure over a wide range of altitudes, and will probe the atmospheres of terrestrial exoplanets. The transiting exoplanet community is joining forces to define a coherent strategy to evaluate JWST's capabilities as early as possible in the mission. In this talk, I will review the observing modes that will be available for transiting exoplanet spectroscopy with JWST and I will present the Transiting Exoplanet Community Early Release Science program.