We report on the design and fabrication of what we call "optical printed circuit board (O-PCB)" by way of interconnecting and integrating micro/nano-scale optical waveguide circuits and miniaturized photonic devices. Planar optical waveguide circuits were fabricated out of polymer materials using thermal and UV embossing techniques. Micro/nano-scale photonic devices include arrayed waveguide gratings, directional couplers, beam splitters, filters, multimode interference devices, micro-ring resonator devices, photonic crystal devices and plasmonic devices. The O-PCBs were assembled by integrating these devices for the functions of transporting, switching, routing and distributing optical signals on flat modular boards. Potential use of O-PCBs for telecommunications, computers, transportation systems, and VLSI photonic circuits are discussed.