<p>This article explores the phenomena of <i>urban fragmentation</i> vis-à-vis <i>urban integration</i>. It analyzes how infrastructure lines such as railways and highways fragment the urban experience and hinder accessibility and walkability in the city. A historical and conceptual analysis of the literature and selected case studies reveals missing – and potential – links in planning theory and practice. The paper identifies four causes of fragmentation – <i>systemic, material, scalar</i> and <i>jurisdictional</i> – and analyzes influential examples of urban (re)integration (e.g. The Boston Greenway, The Cheonggyecheong River and The Highline). Drawing from cases in the Global North in the last 20 years, we categorize archetypical cases of urban fragmentation (i.e. sunken, elevated and fenced-off highways and railways) and strategic and tactical interventions for urban reintegration. Upon examining these projects, we interrogate the <i>paradox of connection</i> and propose a holistic theory of urban integration based on <i>fluid urbanisms, regenerative design, incremental reintegration</i> and <i>intersectorial planning</i>.</p>