The four experiments are committed to developing highly distributed data analysis infrastructures. These infrastructures are distributed both for technical reasons (e.g., to place computational and data resources near to demand) and for strategic reasons (e.g., to leverage existing technology investments). ATLAS and CMS are the most ambitious, anticipating a need for aggregate data rates of ~100 Gbytes/sec, around 60 TeraOps of fully-utilized computing power, and the fastest feasible wide area networks, including several OC-48 links into CERN. Their hierarchical worldwide Data Grid system is organized in "Tiers," where Tier 0 is the central facility at CERN, Tier 1 is a national center, Tier 2 a center covering one region of a large country such as the US or a smaller country, Tier 3 a workgroup server, and Tier 4 the (thousands of) desktops (see figure).