This paper examines the various ways in which migrant settlers have gained and maintained access to land in the informal urban settlements of Wewak, the provincial capital of East Sepik Province, Papua New Guinea (PNG). Urban population growth in PNG and in Pacific Island states more generally is predicted to grow rapidly over the next two decades. Given the limited availability of formal housing for lower income people, it is likely that many will live in informal urban settlements on land owned by customary landowners. To date, there is very little information on how migrants living in informal settlements obtain and maintain access to land to erect dwellings and pursue livelihoods. Drawing on field research carried out in seven informal settlements in Wewak, the paper describes the historical, trading and/or marital ties between landowners and the original settler community. The discussion focuses on how access rights are maintained and have changed over time as the social and exchange relationships deteriorate between second-generation urban migrants and younger-generation landowners. The weakening of the social relationships between these two groups undermines the long-term use rights of migrants. By examining the changing tenure security of second-generation migrants the paper shows that whilst informal land markets perform an important role in housing provision for the urban poor they often fail to deliver long-term tenure security. The paper finishes with a brief consideration of the implications of the research findings for guiding policies on urban land reform and planning on customary land in PNG.