The increasing demand for high bandwidth and density printed circuit boards is the motivation for replacing the traditional electrical connections with optical interconnects to carry high speed data. A new technology Circuits in Plastic (CiP) was developed to implement circuits on plastic substrates using a wide range of plastics. This method offers simple packaging, low cost and environmentally friendly products as well as water-proof circuit boards. This research reports a study of the design, fabrication and testing of multimode polymer optical waveguides formed in transparent substrates suitable for CiP technology. The surface mount electronics components and the optical waveguide are embedded and integrated in a PMMA substrate. The optical signal was coupled directly to/from the optical channel to form the optical circuits in plastic (O-CiP). The technique is also cost effective and environmentally friendly. The performance of waveguides fabricated using five different methods was examined; the coupling loss was found theoretically and experimentally. The propagation loss was less than 0.9 dB/cm which compares well with previous embedded optical waveguides. Furthermore, the bend loss at different bend radii and crossing loss at different waveguide widths were measured. In addition the characteristics of the direct modulated signal in the straight and bent waveguides were investigated including frequency response, group delay and impulse response. A high speed VCSEL and photoreceiver were used to conduct frequency response measurements using butt coupling and lens coupling methods at the receiver side using three different optical wavelengths (850 nm, 1310 nm and 1550 nm).