The ICSID Convention provides a standard for disqualification of arbitrators for lack of qualities of independence and impartiality. However, jurisprudence on the standard of “manifest lack” of qualities in an arbitrator that the Convention envisages is not yet settled as it does not shed much light on what constitutes the terms “manifest lack”. In the recent past, arbitrators have faced frequent challenges regarding their independence and impartiality in relation to the matter at hand. Owing to the absence of clarity in the Convention, this article lays emphasis on the various decisions that have contributed to the change in jurisprudence regarding the disqualification of arbitrators and have introduced a new dimension, akin to certain other arbitration rules. It discusses the three major standards laid down in these decisions for determining “manifest lack” of qualities in an arbitrator under ICSID, namely, the strict standard, the reasonable doubt standard and the very recent, the appearance of bias standard. Further, the article highlights a paradigm shift in the ICSID challenge jurisprudence from an initial stringent requirement of manifest lack towards a linear approach that has contributed to the divergence seen in recent challenge decisions. This article also advocates the need for certain uniform and unambiguous set of rules for effective adjudication of arbitrator challenges in ICSID.