Article Urban Studies 1–17 Ó Urban Studies Journal Limited 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0042098020937987 journals.sagepub.com/home/usj Locating the interstitial island: Integration of Zhoushan Archipelago into the Yangtze River Delta urban agglomeration Huan Zhang College of Civil Engineering and Architecture, Zhejiang University, China Adam Grydehøj Research Center for Indian Ocean Island Countries, South China University of Technology, China Abstract Amidst the debate concerning how to interpret the emergence of new forms of urbanism in today’s world, little attention has been given to urban interstices – the inter-urban boundary areas and interface zones that facilitate exchange between and within vast urban systems. The present paper considers how place is made and developed at these interstices, which frequently provide essential urban functions but are also frequently regarded as rural. We explore this topic through the case of Zhoushan Archipelago (Zhejiang Province, China), an interface zone both between cit- ies within the Yangtze River Delta urban agglomeration and between the Yangtze River Delta urban agglomeration and other megaregions. Like many islands, Zhoushan Archipelago has long been conceptualised as peripheral to the urban yet has simultaneously performed vital urban functions. The paper uses this case to shed light on what interstitiality (in-betweenness) means in today’s urbanism, both for the people living ‘in-between’ and for the wider urban system. Keywords agglomeration/urbanisation, development, infrastructure, islands, planning, transport, Yangtze River Delta Corresponding author: Adam Grydehøj, Research Center for Indian Ocean Island Countries, South China University of Technology, 381 Wushan Rd, Tianhe District, Guangzhou, Guangdong, China. Email: agrydehoj@islanddynamics.org