Prisoners' rehabilitation is not explicitly included in the basic principles of Greek Penitentiary Code; though, it is adopted in several articles of this Code, as well as in other relevant national legislation and international binding legal instruments. In a country where the number of the irregular migrants is estimated circa half a million persons and the proportion of aliens in prisons has climbed above 50% of the total number of prison population during the last years, the challenged issue of the rehabilitation effort especially for irregular migrants, during the execution of criminal sanctions and after their release from prisons, becomes a statistically crucial reality that must be managed effectively. We cannot talk about prisoners' rehabilitation, if we are going to ignore and exclude the most numerous group of them out of the whole effort and procedure. Under this perspective, developing the rehabilitation idea and organizing better its elaboration becomes even more difficult but also more imperative for the penitentiary policy of the country.