The focus of this study lies with irregular migrants who are not in contact with the authorities. Due to their irregular situation, it is difficult to provide information on the numbers of persons that are irregularly staying in Luxembourg. Several actors were able to provide some estimations on the scale of irregular migrants, but these estimations can only ever be partial. Statistics are available concerning the assisted voluntary return and reintegration from Luxembourg programme that is operated by the International Organization for Migration (IOM) as well as concerning the counselling services offered by different non-governmental organisations and associations. However, most of these numbers refer to migrants that are known to the authorities, mainly because they are rejected applicants for international protection.