This book integrates the economics of aging and insight based on political economy and explores generational conflict in the context of governmental spending. This problem is general, as the Covid-19 pandemic has highlighted: lockdowns protect the elderly, but hurt the young. Policies to address global warming impose taxes on the elderly, but would bring benefits largely in the future. This book addresses intergenerational problems by placing its focus on budget allocation, taxation, and regulation. By using Japanese and US data, the authors conduct statistical analysis of whether regions with aging populations may adopt policies that generate benefits during a short period of time instead of policies that could benefit current young generations for an extended period of time. If the policy preferences of voters depend on their age, and if policy adoption by a government reflects public opinion, the change in demographic composition in a region may affect governmental policies. In an aged society, the elderly are pivotal voters. Budgets may be reallocated from policies favored by younger generations, such as education, to policies the elderly prefer, such as welfare programs. This generates an intergenerational externality problem: voters with short life expectancy do not take into consideration long-term benefits. Moreover, the current tax bases may be replaced by other tax bases that do not harm the elderly. The results reported in the book largely support these hypotheses. Evidence also shows that the gender and racial composition and institutional factors, including the extent of fiscal decentralization, are important in anticipating effects of population aging in other countries.