We report on the implementation of novel flexible polymer waveguide interconnects. They are based on newly developed mechanically flexible low-loss silicone waveguides. In addition to meeting the generic requirements of rigid waveguide interconnects, several flex-material challenges were mastered: a) mechanical flexibility permitting waveguide flexing down to radii of 1.0 mm without cracking; b) minimization of waveguide curling induced by the CTE mismatch between flex substrates and polymer layers to enable assembly and connectorization; c) greatly improved cladding adhesion on standard PCB flex substrates, such as polyimide; and d) high environmental stability despite the reduced polymer cross-linking required for better mechanical flexibility. The new waveguides exhibit excellent stability in damp heat (2000 h in 85 °C/85% rH) and under thermal shock (500 cycles from-40° to +120 °C), and lead-free solder reflow up to 260 °C. Using the newly engineered 'Dow Corning WG-1017 Optical Waveguide Clad Dev Sample' and the established 'Dow Corning WG-1010 Optical Waveguide Core', we were able to develop a manufacturing process suitable for large areas and offering high process control and stability to produce waveguides having optical loss values of less than 0.05 dB/cm at 850 nm VCSEL wavelength and fulfilling requirements (a) to (d) above. We describe this manufacturing process and how we have overcome the material challenges mentioned. Furthermore, we present characterization and manufacturing results, show demonstrators, and outline the potential of flexible waveguides as versatile electro-optic assembly platform. © 2013 IEEE.