ATLAS is a particle physics experiment at CERN in Geneva, which will study proton-proton collisions at the highestenergy ever achieved in the laboratory. The main goal of the experiment is to discover the Higgs particle, which is centralto the current theory of how subatomic particles attain mass. ATLAS will also search for a variety of phenomena beyond theStandard Model of particle physics. In order to carry out this research program, ATLAS will collect data from millions ofcollisions per second, recording 200 Hz to tape. This will result??in 3.5 PetaBytes (1015 bytes) of data per year, which coulddouble when secondary data sets are produced. This talk will describe the international computing network (WLCG) thathas been set up using Grid tools to deal with this avalanche of??data. Emphasis will be given to Canada’s contributions to WLCG.