In chapters 6 and 7 I argued that the indiscriminate purchase of sex is unreasonable and that clients who do so owe a duty to affected victims. But to be liable in negligence the defendant’s fault needs to cause the claimant’s injury. As is seen below, contribution to traffi cking by creating demand is almost a textbook example of conceptual and evidentiary diffi culties: very little is known about the way traffi ckers supply victims in response to clients’ demand; the litigation involves both multiple victims and multiple tortfeasors, i.e. each client contributes to the traffi cking of several victims and each victim is traffi cked due to the demand created by numerous clients; any individual contribution is neither necessary nor independently suffi cient to cause the claimant’s traffi cking. In addition, it is not always clear whether the defendant contributed to the traffi cking of any particular victim and the extent of any identifi ed contribution to traffi cking is always unclear. To make things worse, it is not clear whether the injury from traffi cking should be considered as indivisible and what ought to be the scope of liability for contributions which are neither necessary nor independently suffi cient.