This article is based on a data set of over 1,000 judicial decisions in setting aside, recognition and enforcement proceedings. Although sometimes cited as one of the most common grounds for setting aside an award or refusing its recognition and enforcement, the invalidity of the arbitration agreement was raised in less than one-fifth of those decisions. It was confirmed in under one-third of those cases. This article examines which arguments for invalidity were more successful than others and how courts have determined the law applicable to the (in)validity of the arbitration agreement. Notably, less than half of the courts in this data set have engaged in a meaningful conflict of laws analysis. Where they have done so, there does not appear to be a consensus on how the law applicable to the arbitration agreement should be determined and what significance a choice of law clause in the main contract has in this regard.