As part of the Emergency measures in the 1950s, the British colonial government in Kenya introduced regulations that imposed passbooks on the Kikuyu, Embu, and Meru (KEM), who were seen as the wellspring of Mau Mau. Implemented in 1954, the passbook system, which bore resemblance to the formally abolished kipande, restricted the freedom of movement of a population seen as collectively suspect. Like the vipande, passbooks were aimed at controlling the movements of Africans outside their designated native reserves and regulating their ability to work. But the new system, which applied exclusively to those ethnic groups deemed a security threat, further securitized this bottleneck. Passbooks were part of a broader counterinsurgency strategy aimed at screening “unidentifiable” urban residents, sieving the “loyal” from the “disloyal,” restricting the mobility of inhabitants of Central Province, and isolating insurgents and their sympathizers from rights to the city. As I explain in this chapter, passbooks also became a vehicle for an ambitious, if short-lived, attempt at racialized social engineering—aimed at remaking Nairobi’s residents into a “respectable” urban working class based on notions of stable, companionate marriage.