In this paper, a new class of filtering differential phase shifters is proposed and developed, which can provide constant phase shift and self-embedded filtering function at the same time. In contrast to its traditional counterparts, the proposed phase shifter consists of two bandpass filter (BPF) branches and the phase properties of generalized nth-order BPF network are systematically studied at first time. With derived closed-form formula of phase slope, the synthesis method is presented to design the proposed filtering differential phase shifters with prescribed arbitrary phase shift value, passband ripple, and bandwidth. The filter order, which dominates frequency selectivity, is considered in the synthesis design of proposed phase shifter as well. The tradeoff between the frequency selectivity and phase shift is discussed. In addition to the advanced features of multifunction and simple geometry, the proposed filtering differential phase shifters can achieve compact size, low amplitude imbalance, and multiway polyphase capability. To validate the proposed concept and synthesis method, two filtering differential phase shifters with single-phase (90°) and five-way polyphase (45°, 90°, 135°, and 180°) are designed, fabricated, and measured. The simulated and measured results coincide well with the prescribed performances in phase shift and magnitude.