The DIII-D tokamak was a major upgrade of the Doublet III device and was commissioned in 1986. It featured a large noncircular plasma cross section and was optimized for understanding the role of the plasma cross section in plasma stability and performance along with the effective coupling of the plasma to a divertor region for control of the plasma heat and particle exhaust. Active upgrades of the tokamak and facility have kept them in the forefront of fusion research.