By the end of the nineteenth century, the great majority of the civilians living in Gibraltar had, legally, a secure right of residence. But home-grown civilian ministers had to face the challenge of determining who had and who had not unconditional rights of residence, and who else might be let in and on what terms. There was also a siege: the impediments to open access across the frontier with Spain beginning in 1954, and then the closing of the gates in 1969. This plunged relations across the isthmus back to a state not seen since the worst years of the eighteenth century, with serious effects on demographic flows and civilians' sense of their identity. This chapter deals with demography and aliens in Gibraltar during the twentieth century, first describing the Aliens Order Extension Order-in-Council of 1900 and then statutory aliens, British Indians and the Alien Traders Ordinances of the 1920s to 1950s. It also examines the Right of Residence in Gibraltar Ordinance of 1955, the Immigration Control Ordinance, and the Gibraltarian Status Ordinance of 1962 and after.