This Upper House election can be considered a mid-term evaluation of the government in power.
The Diet itself has two chambers -- the Lower and Upper House. Upper House members are elected on six-year, staggered terms.
Only half of the House is up for election every three years, and the House is never dissolved.
Voters cast two ballots - one through proportional representation, and another for a candidate to directly represent their constituency.
The country's 45 districts elect one to six representatives each. All the constituencies colored yellow on the screen are single-seat districts. They tend to swing to one party, making them a key indicator of where the balance of power will land.
Now, let's look at some benchmarks, which will tell us how the Abe administration is faring - once results start rolling in.
Here's the layout of the Upper House, with only those representatives who are in the middle of their six-year terms.
The remaining 124 seats are up for grabs.
The ruling coalition wants to maintain a majority overall --that's 63.
Some senior LDP officials say getting to this marker will show the public is confident in their leadership.
The next benchmark is important for Abe's chances to amend the constitution.
In order to call a national referendum on this issue, Abe will need to maintain two-thirds support.