  The D0 experiment enjoyed a very successful data-collection run at the
Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has
been upgraded to take advantage of improvements to the Tevatron and to enhance
its physics capabilities. We describe the new elements of the detector,
including the silicon microstrip tracker, central fiber tracker, solenoidal
magnet, preshower detectors, forward muon detector, and forward proton
detector. The uranium/liquid-argon calorimeters and central muon detector,
remaining from Run I, are discussed briefly. We also present the associated
electronics, triggering, and data acquisition systems, along with the design
and implementation of software specific to D0.
