We propose a polymer-based microfluidic motherboard that integrates waveguides and fluidic networks provid-ing an interface between microfluidic systems and the outer world. The motherboard facilitates interconnections of several microfluidic chips for multiplexed and simultaneous analysis. It offers a modular network for microfluidic chips, allowing complex microfluidic processes, where each microchip has a particular function. The motherboard includes microfluidic channels machined by micromilling technology and bonded thermally. Waveguides were integrated in the motherboard in the same fabrication process. Additionally, pins were fabricated, which are part of the fluidic interconnections and allow the alignment of a chip with the waveguides of the motherboard. To establish high density microfluidic interconnections between the motherboard and external tubes, reversible PDMS sockets have been utilized. For interconnecting the poly-mer waveguides to the light source and to the detection system, PDMS optical plugs have been developed. To demonstrate the performance of the device, test structures were designed that contained fluidic channels, waveguides and, additionally, custom made o-rings allowing alignment to the connection pins of the motherboard. The single chips were attached to the motherboard by just pressing them onto the alignment pins. A sealed fluidic connection between chip and motherboard is ensured by the deliberate mismatch in diameter between the o-rings of the chip and the pins of the motherboard. The maximally applicable hydraulic pressure before leakage, as well as propagation and coupling losses for the waveguides and optical interconnections have been characterized and tested.