The 2000 UN Trafficking Protocol has obliged states to discourage demand that fosters exploitation that leads to trafficking. Fifteen years later, there is still no shared understanding of what demand means in the context of debates on trafficking in human beings (THB). The terms “trafficking” and “demand” display a lexical and referential ambiguity. This paper provides a history of the occurrence and usage of the concepts “trafficking” and “demand” in the context of debates on trafficking and explores the different meanings and understandings attached to these terms in past and present debates. The paper covers debates on trafficking in human beings since the 1860s and shows that terminological confusion was and still is a constant feature of these debates. The term abolition referred initially to the abolition of state regulation and not – as it is understood in the present-day debates – to the abolition of prostitution. The term trafficking is introduced in past and present debates with a confusing diversity of meanings, referring to the kidnapping of girls for the purpose of prostitution, fraudulent procurement of unsuspecting women for prostitution abroad, procurement of consenting women for prostitution, abetting of irregular border crossing or fraudulent abetting of irregular migration with the purpose of exploiting migrants after arrival and other issues. The term demand was introduced in past and present debates and has a diversity of meanings. It can refer to the biological drive of males, to a demand generated by a system of state regulation of prostitution, to a demand of brothel owners and pimps, or to a demand of male clients to purchase commercial sexual services. Thus, when the issue of demand is raised in debates of trafficking, the meaning attached to the term in a communication context is usually not clear; and the same speaker can often use the term demand rather metaphorically with changing meanings. The paper shows that terminological confusion is effect and cause of ongoing and unsolved controversies about the legal handling of prostitution. The paper shows how the issue of demand originally entered the UN Trafficking Protocol and how subsequent attempts failed to develop an authoritative definition. Although debates are characterised by terminological ambiguity, even the claim that a definition is a necessity is denied. Conceptual confusion hampers mutual understanding, prevents reasonable dispute and undermines the capacity to develop policy approaches which effectively provide protection from trafficking and exploitation. The paper closes with the observation that the controversy surrounding the meaning of demand in the context of anti-trafficking efforts has the effect of raising attention to deal more directly with the issue of exploitation.