IP (Internet Protocol) can potentially become the universal network-layer protocol over all wireless systems as it already is for wireline packet networks. Such an all-IP wireless and wireline network can bring the proven advantages of IP networking to mobile users. However, realizing an all-IP wireless network introduces many challenges, among which is soft handoff. Two major problems need to be solved in order to support soft handoff. First, multiple streams of the same IP traffic have to be distributed via multiple base stations to a mobile station. Second, pieces of data arriving at the mobile station at the same time from different base stations need to be copies of the same data in order for the mobile station's radio system to correctly combine these different pieces into a single copy. A similar problem also needs to be resolved in the reverse direction from mobile stations to base stations. Solving these problems in a distributed all-IP wireless network remains a challenge, although solutions exist for today's circuit-switched wireless systems. This article presents a new approach for soft handoff in distributed all-IP wireless networks. It consists of two main parts. First, a new design of IP-based distributed base stations enables mobile stations in multiple cells to be on the same IP subnet and multiple streams of the same data to be distributed via multiple base stations to a mobile without broadcasting/multicasting and with minimal signaling. Second, a novel IP-layer procedure performed by base stations ensures that the data coming simultaneously from multiple base stations to a mobile station are copies of the same data.