Japan faces a demographic crisis. The rapid ageing of the country’s population, as well as the low fertility rate, means that Japan’s population will suffer a gradual and perceptible decline over the coming decades, unless bold moves are made to address this problem. In addition, the decline in the working age population relative to the large numbers of elderly will place enormous strains on the economy, hindering a sustainable recovery. The ageing problem is symptomatic of the general decline of Japan, with enormous strategic and political ramifications for East Asia. This chapter comprises three sections. The first provides an overview of the twin phenomena of population ageing and decline that together have triggered the demographic crisis in Japan. The second section examines the implications of this crisis from both a human and traditional security perspective. The final section explores some of the measures the Japanese government has adopted to deal with the problem, focusing, in particular, on the issue of immigration. Domestic advocates of large-scale immigration face the challenges of lobbying for an overhaul of government policies in a country where many perceive the presence of foreigners, especially (Asian) undocumented workers, as a threat to public safety and order – with some even seeing them as a threat to national security. 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.