Since its introduction in the early 2000s, reconfigurable optical add/drop multiplexer (ROADM) technology has undergone a series of evolutions. These include the shift to wavelength-selective switches (WSSs), increasing WSS port counts, reductions in footprint, more flexible add/drop, and the move from fixed grid to flexible grid. This white paper explores the component-level and systems-level innovations enabling ROADM evolution along seven vectors related to wavelength capacity-reach, fiber capacity, add/drop and degree flexibility, footprint, openness, operations and manageability, and network availability.