In recent years, the existence of ferroelectricity in a series of two-dimensional van der Waals materials has been experimentally confirmed, in which the ferroelectricity induced by interlayer sliding is an important type. This mechanism is not available in traditional ferroelectrics but can be applied to many two-dimensional materials. In this paper we review the relevant researches and introduce the origin of this type of ferroelectricity: in many two-dimensional van der Waals bilayers, the upper layer is not equivalent to the lower layer, thus giving rise to a net interlayer charge transfer and the inducing vertical polarization to be switchable via interlayer sliding. This unique sliding ferroelectricity can widely exist in many van der Waals bilayers, multilayers and even bulk structures. The interlayer sliding barrier is several orders of magnitude lower than that of traditional ferroelectric, which may greatly save the energy required by ferroelectric switching. At present, this type of interlayer sliding ferroelectricity has been experimentally confirmed in WTe₂ and β-InSe bilayer/multilayer systems, and more systems predicted to be with much stronger interlayer sliding ferroelectricity (like BN) may be realized in near future.