Elections to Japan's upper house, the House of Councillors, are ‘secondary’ elections, that is, elections that do not choose the government. Among the implications of this secondary status is that the party system is primarily determined elsewhere, by the system used in the general elections that do choose the government. From 1947 through 1993 the system used in general elections fostered a multiparty system that did not sit easily with the many single-member districts of the House of Councillors. Since 1996 general elections use a system based primarily on single-member districts, which is fostering a two-party system. As a two-party system emerges, we should expect the single-member districts of the upper house to become more and the multi-member districts to become less congruent with the party system. The 2004 House of Councillors election presented us with our first example of what two-party elections might look like in future upper house elections. The overall results do indeed indicate the advent of the two-party system with the major parties winning 96% of the seats in the district tier and 71% in the PR tier.