In this contribution, we present a review on the various bulk piezoelectric ceramic transformers based on planar vibration modes. The studied transformer shapes include rectangular bar, rings and discs (e.g. disc ring dot) homogeneously poled in the thickness direction. Electrical parameters like transformation ratio, efficiency and input and output power are measured and modelled as a function of frequency and resistive load in the secondary circuit. Analytical modelling has been performed for the "Rosen type" and "ring dot" disc or ring transformers as well as for the bar transformers and several other geometries. Finite element analysis modelling has been performed for the set of other more complicated disc transformer geometries. An overview of the results on the studied transformers is presented, including data on transformation ratio, efficiency and optimum load.