This article discusses formal requirements in open source software contributor copyright assignment and licensing agreements. Contributor agreements are contracts by which software developers transfer or license their work on behalf of an open source project. This is done for convenience and enforcement purposes, and usually takes the form of a formal contract. This work conducts a comparative analysis of how several jurisdicitons regard those agreements. We specifically look at the formal requirements across those countries to ascertain whether formalities are constitutive or probative. We then look at the consequences of the lack of formalities for the validity of those contributor agreements.