For over a decade, some French astronomers visit prisons to talk and discuss about astronomy with prisoners. First we note the paradoxes which exist in the juxtaposition of the words “astronomy” and “prisons”. The importance and interests of these talks are reviewed, as well as the specificities of the audiences. Some material details about the organisation and a brief review of actions done in France today are given. As a conclusion, we emphasize the interest and the utility of these astronomy lectures and discussions.