"This network proposes to develop European expertise in searches for primeval galaxies and in the extraction of key physical information from deep sky observations, to ensure the maximum scientific return of the European instrument NIRSpec on board the future James Webb Space Telescope that will be launched in 2013. The accomplishment of this goal requires the combined expertise of four different communities: 1. Observational astronomers with expertise in deep sky surveys and in spatially resolved studies of distant galaxies. 2. Experts in spectral models of galaxies, to interpret the light emitted by distant galaxies in terms of physical parameters such as star formation rate, metallicity and dust content. 3. Theoreticians with expertise in modelling galaxy formation in its proper cosmological context. 4. Industrial engineers who are responsible for the performance and calibration of NIRSpec. This network will bring together these communities to work on the interpretation of the physical properties of distant galaxies deduced from their spectra and images and to develop practical analysis tools of interest to the exploitation of NIRSpec. It will serve as a training ground for a new generation of young researchers, who will gain broad insights into the problem of galaxy formation --- both in the area of theoretical models and in the preparation and analysis of state-of-the-art observations --- and into the development and implementation of an astronomical space project."