The “humanitarian border” that emerged at the Aegean Islands of Chios and Lesbos during the so called “refugee crisis” arose out of various engagements with care and control. A humanitarian border can be said to consist of the entanglements between humanitarianism and securitization. But how do care and control materialize in practice and how can they move from one place to another? By combining the notion of the “humanitarian border” with the concept of “viapolitics” and an actor-network lens, and based on interviews with state authorities, volunteers and NGOs, this article brings in three claims. First, by studying the “missing masses”, the humanitarian border can be said to arise out of “conjoint actions” that concern engagement with peoples and objects of all sorts. Second, the humanitarian border is not only of a composite nature but of a mobile nature as well. Third, the interstructure of the humanitarian border is generated by a productive relationship between the fluidity of network configurations on the one hand and emerging frictions on the other. By studying the situated tensions between humanitarianism and securitization and focusing on the circulation of materialities of all sorts the movements that make up a humanitarian border can be displayed.