This paper explores the circumstances in which a party might have grounds to challenge the appointment of a party-appointed expert, resulting in the expert’s disqualification or exclusion from proceedings. In assessing the feasibility of such challenges, a number of distinguishing features of these challenges are considered. First, distinguishing the competing rights of the challenging party with those of the appointing party. Secondly, distinguishing the grounds that will justify disqualification of an expert as opposed to grounds that will only affect the weight given to that expert’s evidence. Thirdly, the fundamental distinction between a challenge made to an expert in international arbitration compared with an equivalent challenge in domestic litigation, with the suggestion that a successful challenge is much more likely in the former. And finally, the equally important distinction that must be made between a challenge to a party-appointed expert and a challenge to a neutral, such as an arbitrator or tribunal-appointed expert.