  The CMS Level-1 trigger was used to select cosmic ray muons and LHC beam
events during data-taking runs in 2008, and to estimate the level of detector
noise. This paper describes the trigger components used, the algorithms that
were executed, and the trigger synchronisation. Using data from extended cosmic
ray runs, the muon, electron/photon, and jet triggers have been validated, and
their performance evaluated. Efficiencies were found to be high, resolutions
were found to be good, and rates as expected.
