The ubiquity of Internet access, and the wide variety of Internet-enabled devices and applications, have made the Internet a principal pillar of the Information Society. Decentralized and diverse, the Internet is resilient and universal. However, its distributed nature leads to operational brittleness and difficulty in identifying and tracking the root causes of performance and availability issues. The first step to improve this situation is measurement: illuminating the currently obscure dynamics of the Internet. To address this, we advocate a measurement plane, or mPlane alongside the Internet's data and control planes.mPlane consists of a Distributed Measurement Infrastructure to perform active, passive and hybrid measurements; it operates at a wide variety of scales and dynamically supports new functionality. A Repository and Analysis layer collects, stores, and analyses the collected data via parallel processing and data mining. Finally, an Intelligent Reasoner iteratively drills down into the cause of an evidence, determining the conditions leading to given issues, and supporting the understanding of problem origins.By enabling pervasive measurement throughout the Internet, mPlane benefits everyone: ISPs get a fine-grained picture of the network status, empowering effective management and operation. Application providers gain powerful tools for handling performance issues of their application. Regulators and end-users can verify adherence to SLAs, even when these involve many parties. Customers of all kinds can objectively compare network performance, improving competition in the market.mPlane will significantly advance the state of the art in Internet measurement, from innovative probe technology to intelligent algorithms for distributed data analysis. The development of the Reasoner is a key result that will allow structured, iterative, automated analysis. An emphasis on open, standard interfaces will speed adoption and increase the impact of the project.