Martial law is widely used by governments around the world and yet remains poorly understood. In this article, I aim to expand what we know about the concept of martial law, within the context of the broader literature on emergency powers. This article begins by offering an academic definition of martial law as well as a measurement strategy, generating cross-national, time-series data. This article introduces a novel dataset that records declarations of martial law and states of emergency from 1995 to 2022. I illustrate the utility of this data by showing it can complement research on government repression and overreach.