By Max Deveson
BBC News, Washington
When American voters go to the polls on 4 November, they will not just be choosing a president.
The issue of same-sex marriage has divided opinion in California
In many states, they will also be faced with a number of referendum questions, known as propositions or ballot initiatives. If passed, they will change state laws.
And many of them deal with issues on the frontline of American politics, from gay marriage to abortion.
The most high-profile ballot initiative in this election cycle is probably California's Proposition Eight, or Prop Eight, as it is known for short.
If passed, it would amend California's constitution to say: "Only marriage between a man and a woman is valid or recognised in California."
The proposition has been put forward by opponents of gay marriage in the state, in response to the California Supreme Court's decision in May 2008 to overturn a law introduced by a 2000 proposition, which had defined marriage in state law as being between a man and a woman only.
Opponents of same-sex marriage want to place their definition of marriage in the state's constitution, thus preventing the state's Supreme Court from overturning it.
Although Californian voters opted in 2000 to outlaw same-sex marriage, the battle this year is very tight.
California's Proposition Two would outlaw battery farming
Polls suggest that voters now oppose attempts to amend the constitution, albeit by a very small margin.
Opponents of the measure say they may be helped by the popularity of Barack Obama at the top of the ballot - but also harmed.
Mr Obama will bring out liberal voters who support same-sex marriage, but he will also increase turnout among African-Americans, many of whom oppose it.
Voters in two other states - Florida and Arizona - will also consider constitutional amendments to ban same-sex marriage.
'Right to know'
In California - which has a long history of direct democracy - voters will also be asked to approve measures to raise renewable energy targets, and "prohibit the confinement of farm animals in a manner that does not allow them to turn around freely, lie down, stand up, and fully extend their limbs" - a move aimed at outlawing battery poultry farming.
And Californians will also be faced with a proposition to introduce a so-called "Sarah's Law", which would prevent minors from getting an abortion until 48 hours after their parents or guardians had been notified.
Parents have a right to know about their daughter's abortion
The proposition has divided opinion in the state, with the latest poll suggesting 46% of voters are in favour, with 44% opposed and 10% undecided.
Newspapers in the state are also on opposition sides of the debate: the Los Angeles Times advises a "No" vote, for fear that "some girls will seek out illegal abortions rather than notify their parents", while the Orange County Register urges a "Yes" on the basis that "parents have a right to know about their daughter's abortion".
Two other states will also be voting on propositions dealing with the issue of abortion.
In South Dakota, voters will be asked to approve an amendment to the state's constitution that would ban all abortions in the state except in cases of rape or incest or to protect the woman's health.
And in Colorado, there is a proposition to define "personhood" as beginning at the moment of fertilisation, rather than when an egg is implanted in the uterus.
Opponents of the measure say it would outlaw certain forms of contraception, which prevent implantation (but not fertilisation).
The proposition - known to its supporters as the "Equal Rights Amendment" - is unlikely to pass.
Aside from the issues of abortion and gay marriage, few subjects excite so much passion in US politics as immigration.
Some Americans have become increasingly fearful that - as Hispanic immigration increases - the English language is in decline.
Two states will vote this year on propositions aimed at reversing this perceived decline.
In Oregon, Ballot Measure 58 would prohibit schools from teaching foreign students in their native language after one year in elementary school or two years in high school.
And in Missouri, Constitutional Amendment One would "establish English as the official language for all government meetings where public business is discussed or decided or where public policy is formulated".
Neither measure has much likelihood of being passed.
But, like this year's other ballot measures, they might succeed in bringing people out to the polls, thus helping candidates elsewhere on the ballot.
Indeed, many commentators have suggested that putting controversial propositions on the ballot has been used as an electoral ploy in recent years to bring out the base.
In particular, observers say the large number of anti-gay marriage measures on the ballot in 2004 may well have been put there in order to increase turnout among social conservatives and give George W Bush a boost in the presidential election - a factor which may well have pushed him over the top in marginal states like Ohio.
This year, the Democrats may be attempting to use similar tactics: voters in Colorado and Missouri will be considering propositions on union rights, which could encourage blue-collar Democrats to come to the polls.
In total, there will be 153 propositions or initiatives on the ballot in 36 states this year.
How Americans vote on them will tell us just as much - if not more - about public opinion in America than will the results of the presidential election.