Forced labour has been regulated since 1930 on the basis of the ILO Convention on Forced Labour, and since 1957 on the basis of the ILO Abolition of Forced Labour Convention. In 2000 forced labour was included as one form of exploitation covered by the UN Trafficking Protocol, which situated trafficking into a context of transnational organised crime. In 2014 the ILO adopted a Protocol on Forced Labour, making a link between trafficking and forced labour. The aim of this article is to explore how forced labour came to be regulated and defined in these four treaties. The 1930 ILO Convention came about in a specific historical and political context, yet the 1930 definition remains in use even though the interpretation of forced labour, particularly as it relates to trafficking, has changed. This article focuses on the issue of trafficking for the purpose of forced labour within the context of migration and labour exploitation, and discusses the relevance of historical definitions of forced labour in the current discourse that sees human trafficking mainly as a security threat. It argues that a rigid interpretation of forced labour is not always useful in understanding forms of labour exploitation, at least in a contemporary European migratory perspective. The article calls for a broad interpretation of forced labour, which takes into account also subtle forms of control and coercion.