Parties to an arbitration in the US may challenge an arbitrator or award based on arbitrator bias. Various US arbitration statutes require arbitrator neutrality by permitting parties to challenge an award based on arbitrator bias. The rules of most arbitral institutions also require arbitrators to be impartial and permit parties to challenge an arbitrator's appointment or continued service based on bias. This Practice Note describes the options for parties to challenge arbitral proceedings and awards based on arbitrator bias in arbitrations that US arbitral institutions administer.