This chapter provides an overview of the twin phenomena of population ageing and decline that together have triggered the demographic crisis in Japan. It examines the implications of this crisis from both a human and traditional security perspective. The chapter explores some of the measures the Japanese government has adopted to deal with the problem, focusing, in particular, on the issue of immigration. Japan is in a state of a muted immigration security dilemma; with many people worried about the impact a large influx of migrants would have on what is still a relatively homogeneous nation. The responsibility of elderly care in Japan has traditionally fallen on the family, thereby reducing dependence on the government for maintaining health and living standards. The impact of Japan’s demographic crisis on national security is also evident in the economically induced declining defence budgets over the past decade.