This article introduces Ratio! A Game of Judgment, a card game jointly developed by Dr David Yuratich (the sole author of this article) and Dr Thomas Giddens. Ratio provides an innovative and immersive environment for the deep and active learning of common law legal reasoning. Players adopt the role of a judge and are required to deploy cards representing the main elements of common law reasoning to build a judgment. This article argues that game-based learning (GBL) offers pedagogies which provide an innovative way of engaging and educating law students and explains how these approaches apply to and work within Ratio. It makes a case for the adoption of GBL methods and identifies future research agendas that explore the use of GBL (and Ratio) in the legal classroom.