With exit polls projecting a big win for the Democratic Party of Japan over Japan's long-time ruling Liberal Democratic Party, the BBC looks at the main issues and what separates two very similar parties.
Both parties say the economy is their main focus.
Mr Aso (L) and Mr Hatoyama (R) both say the economy is their top priority
The LDP says it will create 2% growth within two years and two million jobs in three. It also plans to increase household disposable income by one million yen ($10,700; £6,600) in a decade. It says it will raise the 5% consumption tax (the equivalent of value-added tax) to generate revenue, but only when the economy is back on track.
In terms of spending, it says it will fund pre-school education for children between the ages of three and five, and expand student scholarships.
The DPJ says it will not raise the consumption tax for at least four years. It also plans to lower fuel tax and corporate tax for small businesses. It says it can finance spending pledges by cutting waste within the bureaucracy - both in terms of budgetary controls and by reducing the size of the civil service itself.
Its spending plans include the introduction of a child benefit of $3,300 per annum until the child reaches the age of 15. It also plans to introduce a minimum guaranteed pension and abolish compulsory health insurance payments for people over the age of 75.
Both parties want to reduce the number of seats in the lower house, although numbers and timescales are different. They also want to tackle the issue of hereditary candidates.
Both want to ban "amakudari" - the practice whereby civil servants are guaranteed lucrative jobs at public agencies for which they have been responsible. The DPJ also wants to appoint politicians to supervise ministries and in so doing control waste.
Both parties say the Japan-US alliance is at the core of their diplomacy, although the DPJ says it wants to create a "more equal" relationship and review the issue of US military bases in Japan. The DPJ also says it will prioritise better ties with regional neighbours. Both parties promise to take a tough stance towards North Korea.
The LDP says it wants look at revising Japan's pacifist constitution, which prohibits the retention of armed forces for anything other than self-defence. It also wants to pass a law allowing the despatch of its troops overseas. It will also continue the refuelling mission in the Indian Ocean - something the DPJ has indicated it will stop.