This Ph.D. thesis examines the colonial efforts aimed at increasing and physically improving the native population in Portuguese Angola from the late nineteenth to the mid-twentieth century. It argues that, throughout this period, these / thus far under-researched / efforts were diverse and inextricably linked to the pervasive idea of a demographic crisis: due to alarming reports on epidemic and endemic diseases, high infant mortality rates and mounting emigration flows, many colonialists feared that the native population was declining, and that this endangered both the economic development of the colony and the legitimacy of Portuguese colonial rule. While critically assessing this depopulation discourse and the role played in it by scarce but widely used demographic knowledge, my analysis focuses on the ideas, policies and practices that were conceived and implemented by colonial administrators, doctors, missionaries and scientists in order to 'stem the tide'. I pay particular attention to the colonial response to sleeping sickness from the late nineteenth century onwards and the establishment of a broader system of African healthcare after the First World War. I also look at colonial attempts to resettle the rural population into model villages, to reduce long-distance labour migration and to curtail emigration to neighbouring colonies. This study reveals that the impact of population politics in Angola often remained more modest than planned, insofar as their implementation was severely hampered by the 'weakness' of the colonial state and by the attitudes and actions of many Africans themselves. These last did often not approve of Portuguese goals and methods and sought to evade medical and administrative control. Moreover, this dissertation consistently argues that both the discourse of population decline and the particular policies conceived and implemented were not unique to Angola. They were embedded in and shaped by broader contemporary debates and practices that transcended colonial and imperial boundaries.