The proposed project deals with one of the major open problems of Astroparticle Physics and Cosmology. The star and galaxy formation history has built up a diffuse extragalactic radiation field in the ultraviolet to infrared wavelength regime. Direct measurements of this extragalactic background light (EBL) are difficult. The observation of distant sources of GeV-TeV photons using Imaging Air Cherenkov Telescopes (IACTs) can provide an indirect measurement of the EBL due to attenuation via pair production. The observed spectra therefore carry an imprint of the EBL. MAGIC II is a system of two IACTs starting data taking in Spring 2008. The energy threshold of the MAGIC II will be 50 GeV. One of the key elements to achieve the low energy threshold and high sensitivity is a novel ultra fast readout system combined with a novel analysis technique using timing information. Essential is also the fast access to large samples of data which will be possible using the new MAGIC II datacenter at the host institution. With the high sensitivity and the low energy threshold of the MAGIC II, it will be possible to detect many extragalactic sources of gamma-rays located up to the redshift of z=1. The measurement of precise gamma-ray spectra of many extragalactic sources provides a unique opportunity to study the evolution of the EBL. This evolution is not accessible otherwise. The applicant will be involved: A) in the commissioning of MAGIC II, specifically in the novel readout system in order to lower the energy threshold; B) in development of a novel analysis technique to increase the sensitivity; and C) in a detailed study and precise measurement of the evolution of the EBL up to a redshift of about z=1. This will be the first time that the evolution of the EBL level can be studied. Constraints on Cosmology models and on galaxy evolution scenarios are anticipated from this project.