I still remember very clearly my first encounter with peer review: I was a Ph. D. student in physics and I had written my first paper, submitted it to a journal and - after what seemed to me a very long time - received a reply with the request for few changes and corrections I was supposed to include in my paper before it could be considered for publication. These very simple steps: the writing up of some original research results in a paper, its submission to a journal and the process of the work being read and judged by someone reputed to be an expert in the field is what we call peer review - the judging of scientific work by your peers - and it is an essential part of what science is. No scientific achievement can be considered as such until has been recognized by the community at large and such a recognition mainly comes from the peer review process. The presence of this check has arguably helped and fostered the constant and cumulative growth of science.