Agreement on the definition of human trafficking was reached in 2000 with the adoption of the Protocol to Prevent, Suppress and Punish Trafficking in Persons Especially Women and Children, supplementing the United Nations Convention against Transnational Organized Crime.1 The Convention defines trafficking in persons as the recruitment, transportation, transfer, harbouring or receipt of persons, by means of the threat or use of force or other forms of coercion, of abduction, of fraud, of deception, of the abuse of power or of a position of vulnerability or of the giving or receiving of payments or benefits to achieve the consent of a person having control over another person, for the purpose of exploitation.2The definition includes three elements that must be fulfilled for conduct to amount to human trafficking, namely, an act, a means, and a purpose.3 Despite the apparent consensus, discussion has continued as to the definition’s precise scope,4 and the relationship between the concept of trafficking and related concepts, such as slavery, servitude, and forced labor.5 On the relationship between trafficking and forced labor, the International Labor Organization’s (ilo) position is that “trafficking in persons for the purpose of exploitation is encompassed by the definition of forced or compulsory labor.”6 Moreover, the 2014 Protocol to Convention No. 29 on Forced Labor explicitly requires efforts to combat trafficking for the purpose of forced labor.7 Notably, Stoyanova regards the ILO’s position as an “erroneous” one.8 These differing positions demonstrate that consensus on the conceptual boundaries of each of the elements of trafficking has yet to be reached. In S.M. v. Croatia, the European Court of Human Rights’ (ECtHR) Grand Chamber engaged anew with the discussion on trafficking and its conceptual proximity to or overlap with the terms in Article 4 of the European Convention on Human Rights (ECHR), namely, slavery, servitude, and forced labor. The issue centred upon whether Croatia had fulfilled its procedural obligations under Article 4, and the holding of the Court on this matter should not be overlooked.9 The focus in this article, however, is the Court’s analysis of the material scope of Article 4, especially the place of trafficking within such material scope; the connection between trafficking and forced labor; and the relationship between exploitation of prostitution, forced labor, and trafficking.10 With previous case-law on trafficking and Article 4 having attracted criticism,11 the task faced by the Grand Chamber was to take a step in the direction of clarity. Although it has succeeded in doing this to an extent, the question is whether the clarity that has been achieved is being built on an unstable foundation.