We present a review of our research results on the thermal or ultraviolet (UV) imprinting of micro/nano-scale polymer optical waveguides of diverse nature and dimensions for the fabrication and integration of an optical micro-system that we call optical printed circuit board (O-PCB), which are made in hard and flexible forms of generic and application-specific nature. Micro/nano-photonic devices, like micro-lasers, sensors, couplers, splitters, filters, micro-ring/racetrack resonator devices, photonic crystal devices, and plasmonic devices are interconnected and integrated using imprinted polymer waveguides to perform the functions of sensing, storing, processing, transporting, switching, and distributing optical signals on the O-PCBs. We describe the detailed process of designing, imprinting, fabricating, and integrating waveguides and discuss on the scientific and engineering issues and challenges thereof.