Abstract: The state-of-the-art developments of substrate integrated waveguide (SIW) techniques is overviewed. Various SIW-based passive and active components reported so far have demonstrated that they can be effectively integrated in the form of low-cost system-on-substrate (SoS), which provides complete packaged system solutions. Different innovative SIW beam-forming techniques are discussed. Future developments are forecasted, which suggest the expansion of substrate integrated circuits (SICs) into 3-D geometry and mixed integrations of dissimilar waveguides within the same substrate building blocks. Other SIW-related trends are also described, including non-linear and active waveguide developments as well as CMOS-based waveguide synthesis for millimeter-wave and THz applications.