Commissioning the CMS experiment

The CMS experiment is getting ready to take data at the LHC accelerator at CERN. Due to late delivery of the experimental caverns the detector had to be pre-assembled on the surface and lowered in large segments. This has constrained the commissioning strategy of the experiment. Global commissioning has started in Spring of 2007 and has progressed in parallel with the construction and assembly of detector and services underground. This paper describes the strategy adopted in order to commission components of the system in incremental steps in order to be ready to accept collisions from LHC with a well debugged and understood system, including the detector, acquisition system, trigger, software, computing and data shipping.