In 2005, the International Labour Office (ILO) published its first global estimate of forced labour.1 The estimate (a minimum of 12.3 million persons in forced labour at any point in time in the period 1995-2004) received considerable attention by governmental and non-governmental organizations and in the media. It has since been widely cited as the most authoritative estimate of the largely hidden, and therefore difficult to measure, phenomenon of forced labour.