We present results on the commissioning and performance of the CMS electromagnetic and hadron calorimeters in pp collisions at a centre of mass energy of 7 TeV at the LHC. The first LHC beams have been used to finalize the commissioning of the readouts and triggers. The calibrations and synchronisations of the calorimeters using cosmic muons, beam splash events (where the LHC beam is targeted on upstream collimators), and collision data including reconstructed physics objects are presented. The quality of the offline data reconstruction, from low level quantities to showers, has been investigated and optimised using known physics processes. In-situ data and thorough data/MC comparisons have been used to measure and tune the detector performance. First performance results are given.