Phase-shifting Digital Holography（PSDH），which combines phase-shifting technology with digital holography， provides a fast， non-invasive， and high-precision approach for the three-dimensional morphology or refractive index distribution of microscopic objects. Compared with the off-axis digital holography， the phase-shifting on-axis digital holography makes full utilization of Spatial-bandwidth Product （SBP） of the CCD camera. The conventional phase-shifting digital holography needs to records multiple phase-shifting holograms in a step-by-step manner， from which the artifact-free phase and amplitude images of a sample can be reconstructed. To enhance the imaging speed of PSDH， parallel phase-shifting technique （or simultaneous phase-shifting technique） was proposed， with which multiple phase-shifting holograms can be obtained at the same time. In this paper， the concept and implementation of phase-shifting technologies are introduced firstly. Then， three different approaches of parallel phase-shifting， which are based on multiple CCDs， pixelated phase-mask， and parallel beam-splitting， are reviewed. Eventually， the applications of parallel PSDH in the biomedical field， air/liquid flow visualization， surface topography， micro-/nano-scale device inspection are introduced.