A review is given of techniques to integrate passive and active, optical and optoelectronic, functions within one photonic circuit. Different platforms have been developed to realize these circuits in a planar geometry on an indium phosphide substrate. The physical background of these techniques will be described and an evaluation will be given regarding their strong and weak points. An in-depth treatment will be given of two of the integration techniques, which have not yet been thoroughly described in literature: a polarization-based integration scheme (POLIS) and an active-passive regrowth technique. Finally, an outlook on the future of the different photonic integration techniques is presented.