  This is a proceeding of the CERN Latin American School of High-Energy physics
that took place in the beautiful city of Natal, northern Brazil, in March 2011.
In this paper I present a review of the main topics associated with the study
of Heavy Ion Collisions, intended for students starting or interested in the
field. It is impossible to summarize in a few pages the large amount of
information that is available today, after a decade of operations of the RHIC
accelerator and the beginning of the LHC operations. Thus, I had to choose some
of the results and theories in order to present the main ideas and goals. All
results presented here are from publicly available references, but some of the
discussions and opinions are my personal view, where I have made that clear in
the text.
