Photon circuits are light conducting networks formed by joining several dielectric waveguide channels for the transmission of light. Their production utilizes the most advanced surface technologies and represents one of the most important challenges for the next decade. These circuits are usually monomode when the lateral dimensions of the conducting wires are small compared to the photon wavelength. In this chapter, we deal with monomode circuits where the interfaces between the different wires, out of which the circuits are made of, play a fundamental role. All such circuits exhibit a variety of interference effects in their transport properties. The emphasis in this chapter is placed on the network creations, which include barriers, stubs or resonators, closed loops, interconnecting branched networks, and multiplexers. Results for the transmission and reflection properties of such circuits are discussed in terms of the wavelength of the excitations and the physical properties of the circuits.