Despite common socio-demographic pressures such as longer longevity, lower fertility rate, and feminization of labor market, public elderly care policy is remarkably diverse across advanced industrialized countries. This dissertation is an attempt to explain the cross-national variation of elderly care programs from the perspective of historical institutionalism. Specifically, it maintains that the statesociety relations structured by electoral rules and party system affect the development of elderly care programs. Since universalistic social policy, including public elderly care programs, faces collective action problems, it is less likely to thrive unless the state relatively autonomous from societal interests is able to coordinate its benefits and costs in an equitable way. And, then, to what extent the state retains its relative autonomy is contingent on the predominant mode of intra- and inter-party competition in each country. On the intra-party dimension, whereas personal-vote-oriented electoral rules create a decentralized party and clientalistic political competition through particularistic benefits, party-vote-oriented electoral rules generate a centralized party and party-based political competition. On the inter-party dimension, while a ruling coalition fragmented along various social cleavages promotes particularistic party competition, one-party dominance is capable of internalizing the benefits and expenses of social protection programs within its broader constituencies unless the dominant party itself is decentralized. Hence, this thesis claims that oneparty dominance under the party-vote-oriented electoral system allows the state to be autonomous from societal interests and expand public elderly care programs. To verify the above theoretical argument, this thesis conducts quantitative as well as qualitative analysis. Its quantitative analysis, using pooled cross-section and timeseries data of 15 OECD countries from 1980 until 2001, shows that electoral rules structure the process translating demographic changes into public spending for elderly care programs. Qualitative case studies, which cover Sweden, Japan, and the U.S., demonstrate that the state plays a critical role in developing and reforming public elderly care programs in these countries. Overall, this thesis concludes that although the effects of party system are inconclusive, the degree of state autonomy structured by electoral rules is an important determinant of public elderly care policy.