In this paper, a class of 3D bandpass frequency selective structures (FSSs) using stacked planar slotlines is proposed to exhibit bandpass filtering response of high performance. Firstly, a traditional slot-type frequency selective surface and the proposed stacked planar slotlines are introduced successively, and their operating principles are discussed to provide a comparison with each other. Then, two design examples on the basis of the stacked slotlines are presented to exhibit bandpass response with wide out-of-band rejection and high frequency selectivity, respectively. It is found that the stacked slotline structures can produce controllable multi-mode resonance and be exactly analyzed by using transmission-line theory over a wide frequency range.