This lecture gives an overview of the design and current status of the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC). After a short introduction of the physics goals and design of the detector, the modular building of the detector is discussed as well as its commissioning using cosmic rays and beam induced muons from the first circulating LHC beams in September 2008. While eagerly anticipating the upcoming restart of the LHC, the CMS collaboration has invested a serious effort in studying the performance of the CMS detector as a scientific instrument using cosmic-ray data from a sustained run with full detector in readout and magnet switched on: the Cosmic Run At Four Tesla (CRAFT), recorded during a month-long campaign in October and November 2008. This was a crucial step towards the commissioning of CMS and understanding of the detector performance, improving the level of preparedness of CMS for physics analysis. The precise mapping of the CMS magnetic field using cosmics rays is highlighted as an example of a successful improvement that resulted from the analysis of the CRAFT data.