Early on the Universe consisted of a near-uniform mixture ofhydrogen, helium, dark matter and radiation. The emergence ofstructure from a stochastic background of fluctuations in theperiod between 400.000 years and 1 billion years is the main subjectof this proposal. This era saw the formation of the first autonomous sourcesof radiation, stars and black holes. This `renaissance' of light led to the heating,reionization and pollution of the Intergalactic Medium with metals.We will unravel how the hydrogen in Universe progressed from substantially neutral to highly ionized by detailed comparison of cosmological hydro-simulations of the Intergalactic Medium (IGM) and galaxy formation including continuum and resonant Lyman-alpha radiative transfer with QSO absorption spectra and LBG/ Lyman-alpha emitter surveys and other data.This will help us to make the most out the wealth of information which will be provided by new observational missions and surveys which have just begun (or are just about to begin) to report results (UKIDDS, VISTA, Planck, Herschel, COS@HST, LOFAR, ALMA). In this way we expect to make decisive contributions to the expected transformation of our understanding of this exciting period in the history of the Universe.Measurements of the matter power spectrum on scalesfrom 1Mpc to a Gpc from Lyman-alpha forest, weak gravitational lensing,and galaxy survey data contain important information of thenature of dark matter and the mass and number of species ofneutrinos. Particularly exciting is the possibility to significantly push thelimit on 'how cold' dark matter is. To robustly answer the question, whether the free-streaming of dark matter suggested to solve the dwarf-galaxy problem of the cold dark matter paradigm is consistent with Lyman-alpha forest data, is another key goal of this proposal.