We present an over of our work on the micro/nano-scale design, fabrication and integration of optical waveguides and photonic devices for optical printed circuit board (O-PCBs) application. The O-PCBs consist of planar circuits and arrays of waveguides and devices of various sizes and characteristics to perform the functions of transporting, switching, routing and distributing optical signals on flat modular boards. We have assembled O-PCBs using optical waveguide arrays and circuits fabricated via embossing of polymer materials. The waveguides optically interconnect various photonic devices like directional couplers, multimode interference devices, light sources, detectors, and filters. We use specially designed microlenses, 45-degree mirrors and curved mirrors to maximize the light coupling efficiency between devices. The information handling performances of the O-PCBs are measured up to 10 Gbps. For nano-scale photonic integration and applications, we designed power splitters, wavelength splitters, and waveguide filters using photonic crystals and plasmonic waveguide structures. We discuss scientific issues and technological issues concerning the miniaturization, interconnection, and integration of micro/nano-photonic devices and circuits and discuss potential utilities of O-PCBs and micro/nano-photonic modules for applications in computers, telecommunication systems, transportation systems, and bio-sensing microsystems.