  The ATLAS detector at CERN's Large Hadron Collider will be exposed to
proton-proton collisions from beams crossing at 40 MHz that have to be reduced
to the few 100 Hz allowed by the storage systems. A three-level trigger system
has been designed to achieve this goal. We describe the configuration system
under construction for the ATLAS trigger chain. It provides the trigger system
with all the parameters required for decision taking and to record its history.
The same system configures the event reconstruction, Monte Carlo simulation and
data analysis, and provides tools for accessing and manipulating the
configuration data in all contexts.
