This year marks the 20th anniversary of IBM's announcement of its impending plans to insert CMOS/Cu BEOL technology into production, and its having shipped the first functional CPU prototypes. The subsequent manufacturing ramp in mid-1998 provided the first commercial IC chips with Cu BEOL. This invited paper covers the timeline of this technology, with its key defining elements, subsequent innovations, and likely future directions. The original, basic features of this technology have endured to this day, though with many evolutionary improvements. But now, in its 10th generation of manufacturing, and 12th in research, we are finally seeing changes beyond evolutionary. The replacement of Cu metal for the finest wiring levels may occur over the next 1-3 nodes.