The Duomatic principle is a well established part of corporate law, enabling shareholders to informally but unanimously make decisions which bind the Company. It traces its history to some of the earliest cases of company law, and the most recent review of company law decided to leave it uncodified. The resulting flexibility has caused some uncertainty as to the precise ambit of this principle. The aim of this thesis is to establish how this principle should interact with modern corporate law, review the judicial history of this principle and provide a modern test for its application. In order to do so, it firstly reviews the background to the modern corporate form, to establish where this principle should fit into the modern decision making framework for a company. It then traces the history of the principle, from its origins in Salomon and partnership law to its modern day application, and compares the judicial treatment of this principle to the normative framework. It then develops the modern, practical test for judicial application of this principle: when the principle can apply, and who needs to do what to make it do so. However, this test seems unsatisfactory as on almost every subject there are cases that conflict with this general position: whilst a modern test can be constructed, there is no certainty that it will be followed. This thesis ultimately concludes that this principle is a subset of equity; a remedy that courts retain discretion to utilise should they see fit and so not one of objective verifiable application – a position which conflicts with the theoretical root of the principle and its apparent modern day application.