  The trigger system of the Surface Detector (SD) of the Pierre Auger
Observatory is described, from the identification of candidate showers ($E>1$
EeV) at the level of a single station, among a huge background (mainly single
muons), up to the selection of real events and the rejection of random
coincidences at a higher central trigger level (including the reconstruction
accuracy). Efficiency of a single station trigger is evaluated using real data
, and the high performance of event selection hierarchy will be demonstrated.
