The Convention Implementing the Schengen Agreement of 14 June 1985 (CISA) firstly set down the Schengen Information System (SIS) to remedy the security gaps caused by the abolishment of controls among the States’ borders. Thus, most SIS alerts supported the States’ activity in the fields of police and criminal judicial cooperation. After the communitarisation of the SIS in the European Union (EU) and the European Community (EC) acquis, the SIS was revised twice. These reforms have progressively distorted the nature of the SIS to prevent and fight irregular migration. This post traces the development of the SIS under the intergovernmental and supranational legal frameworks to point out how the new SIS alerts on return mark a change of course in the objectives pursued by the SIS second-second generation and, consequently, in the policies underlying its implementation too.