"Cosmology has entered the precision era, now cosmological data can be used to test fundamental physics. There are 4 area where this interplay between physics and astronomy is particularly important: the nature of dark matter, the neutrino mass, testing inflation and unveiling the nature of dark energy. To address some of these fundamental issues we have build the Atacama Cosmology Telescope (ACT, firts light 2007): a 6 m radio telescope located in the Atacama Plateau in Chile. ACT will map about 200 square degreees of the Cosmic Microwave Background (CMB) in three bands with unprecedented resolution and sensitivity. This is accompanied by a vigorous follow up effort in other wavelenghts (X-ray/optical/UV/IR). These maps can be used not only to study the primary CMB but also to study the secondary CMB. The interveening cosmological structures leave their imprint on the CMB fluctuations through several effects(Rees-Sciama, thermal and kinetic Sunyaev-Zeldovich effects, gravitational lensing). These signals can be used to constrain the neutrino mass, testing inflationary models by measuring the shape of the primordial power spectrum and investigating the nature of dark energy with many complementary techniques. We propose to develop the techniques to analize ACT data and to carry out the analysis."