Abstract: Hallmark is a project being developed by U.S. Defense Advanced Research Projects Agency (DARPA) for solving a series of key technology of space command and control, which will provide U.S. high level leaders with tools for real-time understanding and assessment of space situation. The development background and goals of Hallmark are firstly introduced. Then the main technology and progress of Hallmark are summarized by technical areas|tools and capabilities development, testbed development and integration, demonstration and evaluation. Finally, five revelations are proposed to research space command and control.