The right to challenge an arbitrator is an essential part of arbitral due process. The challenge procedure depends on whether it is carried out in ad hoc arbitration or institutional arbitration. This paper explores the differences between the challenge procedures in both ad hoc and institutional arbitration. In addition, an analysis of the problems associated with the procedures is included. Finally, even if the right to challenge should be limited only to those cases in which there is a real threat to the integrity of the arbitration procedure, this right to challenge the arbitrator is often misused by the parties to delay the proceedings and postpone a negative decision of the dispute. That is why the parties have to primarily anticipate this when concluding the arbitration agreement and should regulate the situation when a party raises a challenge to an arbitrator. When they do not obey it, they have to count on the rules which govern the proceedings. In ad hoc proceedings, it can be recommended for the parties to agree on some rules for ad hoc proceedings, e.g. UNCITRAL Arbitration Rules. These are tailor-made procedural rules for ad hoc arbitration that also provide for rules of challenge procedures. The UNCITRAL Rules are examined for their ability to meet the challenges discussed in the current, non-standard system.