Why hold the elections?

They were called mid-terms because they come half-way through the four-year term served by a president, though the elections were in fact for Congress - the two houses of the US legislature. This time, there were also races for 36 of the 50 state governorships as well.

In Congress, all 435 members of the House of Representatives faced the voters, as they do every two years.

But only one third of the 100 members of the Senate are up for election at any one time. That translated into 34 seats this year - 20 Republicans and 14 Democrats.

Why not elect everybody at the same time?

The American system was designed to be overlapping both in terms of the powers of the different bodies and in terms of when people are elected to them.

The House of Representatives is the larger of the two Houses of Congress. It was set up as a popular body with the number of members tied to the size of the population. The idea was for it to directly and quickly reflect the public mood, which is why the members face election every two years.

The Senate was planned as a more reflective body and each state has two senators regardless of its size. Senators serve for six years. Every two years, one third of them face re-election.

Who controls what following the elections?

President George Bush's relentless campaigning for candidates around the country has paid off - the Republicans have control of both the Senate and the House of Representatives.

Ahead of the elections, the Democrats had a single majority in the 100-seat Senate. But, early on Wednesday, the Republicans captured their 50th Senate seat in Missouri. Because Vice President Dick Cheney is able to cast any tie-breaking vote, the Republicans now have effective control of the chamber.

Also ahead of the elections, the Republicans had a slim majority in the House of Representatives.

They controlled the House with 223 seats to the Democrats' 208. But this lead now looks likely to increase.

What were the key contests?

Among the tight contests were: