Tunable diplexers in three-dimensional (3D) integrated circuits (IC) (3DIC) are disclosed. In one embodiment, the tunable diplexer may be formed by providing one of either a varactor or a variable inductor in the diplexer. The variable nature of the varactor or the variable inductor allows a notch in the diplexer to be tuned so as to select a band stop to eliminate harmonics at a desired frequency as well as control the cutoff frequency of the pass band. By stacking the elements of the diplexer into three dimensions, space is conserved and a variety of varactors and inductors are able to be used.