"Rarely in astrophysics are there opportunities to spectrally classify a completely new group of astrophysical objects. This is the challenge facing the exoplanets christened “hot Jupiters”. The detection and subsequent spectroscopic information now achievable for a large number of these exoplanets are now allowing for detailed comparative exoplanetology. This project uses a twofold approach to advance both the theory and observation of these exoplanets beyond their current limitations. Hot Jupiter atmospheric spectra are built from two large observational survey programmes headed by Dr. Sing to obtain a vast amount of high quality data on transmission spectra. One large programme uses the HST which alone will quadruple the number of broadband exoplanet transmission spectra. The Hubble survey will be augmented by a large programme on the GTC telescope, where we will put efforts into pioneering multi-object spectroscopy, capable of delivering space-like quality spectra. Both large programmes will be further complemented by followup observations, as well as existing near-IR spectroscopy. This project will combine this plethora of data in a coherent fashion, enabling studies of nearly the entire planetary atmosphere. Our observational efforts will be combined with a broad and inclusive theoretical modeling programme, where we will incorporate clouds and hazes, modelling the complete atmosphere in a self-consistent manner with a 3D global circulation model. Our library of transmission spectra across the hot-Jupiter class will be used to address long outstanding and complex issues. We will focus our efforts on two key areas, addressing why some hot Jupiters have hazes & clouds while others do not, and the outstanding issue on the presence or absence of stratospheres. For the first time a comprehensive set of high quality exoplanet spectra will be available with which to inter-compare using the required set of theoretical tools."