The routing phase follows the placement phase. It determines the course of the wires that connect the cells laid out during the placement. The structure of the routing phase depends greatly on the design and fabrication technology. There are two approaches to routing—two-phase and area routing. In area routing, the routing process is carried out in one phase that determines the exact course of the wires. In two-phase routing the routing phase is subdivided into the global (or loose) routing phase—which determines how wires maneuver around and through cells—and the detailed (or local or homotopic) routing phase—which determines the exact course of the wires. We now describe both approaches to routing intuitively.