This dissertation is an ethnography of the social as it is imagined, constructed and critiqued by public healthcare professionals in the Metropolitan Region of São Paulo (RMSP), Brazil. These professionals are the builders and operators of the world’s largest universal healthcare system, the Unified Health System, known by the acronym “SUS”. Set in the metropolitan context of RMSP, and the democratic context of post-1985 Brazil, this ethnography is a meditation on the reasoning practices through which healthcare professionals construct the social by grappling with the material challenges of producing healthcare access in Brazil’s largest and wealthiest metropolis. Ultimately, I argue that my interlocutors’ visions of the social are “logistified” and that they are logistified in particular ways. Across four problems – one per chapter – the dissertation traces the ways that health figures as a field for the co-production of social orders through the assertion of logistical objects, techniques and qualities. Material ephemera like files, patients and pharmaceuticals are expected to “flow” according to mediating logistical frameworks that are always changing. Through what I call “logistical reason”, my interlocutors enact and critique such frameworks by attaching value to particular qualia of mobility, scale and order. I take these enactments, in turn, to demonstrate local grammars of logistical commonsense. This ethnography poses the logistical as an analytic question rather than a premise or conclusion. It attends to moments and spaces in which professionals think with material ephemera to instantiate the social in logistified forms. Through attention to speech, embodiment, materiality and imagination, I show that logistical reason is not a reductive mindset but rather an active, fertile disposition. Radical activists and conservative policymakers alike “experiment” and “innovate” through logistical reason to produce ever-reforming arrangements of health and the social in RMSP. By examining these “experiments”, Sciences of São Paulo “reassembles” the social ontology upon which reason, science and politics rely in contemporary RMSP. Highlighting my interlocutors’ imaginative engagements with mobility, scale and order, I offer an ethnography of health logistics that is rooted the everyday qualia of metropolitan social life. The dissertation is based on ethnographic material developed over the course of two years in RMSP (2016-18), during which time I took graduate classes in public health; participated in conferences, protests, and workshop discussions organized by activists and academics; met with experts in health law, finance, informatics and policy; and conducted fieldwork in the primary care network of Terraville, a municipality outside of São Paulo proper. The resulting ethnography is divided into two parts. Part 1 explores the sciences of “collective health” – the Brazilian offshoot of “Latin American social medicine” – in RMSP. This first half of the dissertation engages with activist-scientists known as “sanitaristas” as they interrogated the mixed success of several universal health technologies. In Part 2, I turn to spaces of administration and policymaking in São Paulo and Terraville to explore how logistical reason was enacted in the everyday work of non-activist professionals. Across four chapters, I document how professionals enacted logistical reason in engagements with a range of technologies.