For many voters, a presidential candidate's position on abortion -- anti-abortion activists or abortion rights activists -- is a defining issue. Here is how the 18 candidates for the White House in 2008 come down on the issue.

Democrats

Biden

Sen. Joe Biden said in the April presidential primary debate, "I strongly support Roe v. Wade." Biden, a practicing Catholic, accepts his church's view on abortion but says he will not legislate to support it. He did vote in favor of banning late-term abortions in 1999, saying there is "clearly viability" in late-term, unborn fetuses, but decried the recent Supreme Court's explanation upholding the ban. Biden said it was not so much the decision, which he agreed with, but the way it was explained by the court. "This is all code for saying, 'Here we come to undo Roe v. Wade,'" he said. Biden also signed a letter with 58 other senators urging the president to expand stem-cell research.

Clinton

"I am and always have been pro-choice," Sen. Hillary Clinton told the New York Times in 2000. She is supported by many pro-choice advocacy groups including NARAL and EMILY's List. Clinton voted against banning partial-birth abortions, which would make exceptions if a woman's life was in danger but not if her health was. "I can support a ban on late-term abortions, including partial-birth abortions, so long as the health and life of the mother is protected," Clinton said in a senatorial debate in 2000. Clinton also signed the letter to President George W. Bush requesting governmental expansion of stem-cell research.

Dodd

"I happen to believe a woman has a right to choose," said Sen. Chris Dodd in a 2007 Presidential debate. Supported by NARAL, a pro-choice advocacy group, and with a record opposing partial-birth abortion with exceptions made only if a mother's life is in danger, Dodd has a strong voting record which supports his pro-choice stance on abortion. Dodd supports expanding embryonic stem cell research in America and signed a letter to Bush urging him to do so.

Edwards

Former Sen. John Edwards has established himself as a pro-choice contender in the 2008 race. In the Democratic debate on April 26, 2007, Edwards said, "The kind of people that will be appointed to the US Supreme Court by the next president will ontrol whether a woman's freedom, freedom to choose, make her own health care decisions will be made by her or will be made by the government or by some men sitting on the US Supreme Court. Now, on the issue of abortion, I believe in a woman's right to choose, but I think this is an extraordinarily difficult issue for America." Edwards has also shown his support for expanded embryonic stem cell research.

Gravel

In a press release on April 27, 2007, former Sen. Mike Gravel stated, "Any decision on abortion should remain between a woman and her doctor. There is no room for interference from politicians and judges." Gravel is an advocate for embryonic stem cell research, telling the Blue State Observer that to limit scientific advancement is wrong.

Kucinich

Rep. Dennis Kucinich was originally an abortion opponent, but shifted his views years ago after Congress began severely limiting abortion. In a presidential debate in 2004, Kucinich said, "I've always worked to make abortions less necessary, through sex education and birth control. But the direction that Congress has taken, increasingly, is to make it impossible for women to be able to have an abortion if they need to protect their health. So, when I saw the direction taken, it finally came to the point where I understood that women will not be truly free unless they have the right to choose." Kucinich is supported by pro-choice organizations. He has also voted in favor of embryonic stem cell research.

Obama

In the 2007 Democratic primary debate, Sen. Barack Obama said, "I think that most Americans recognize that this is a profoundly difficult issue for the women and families who make these decisions. They don't make them casually. And I trust women to make these decisions in conjunction with their doctors and their families and their clergy." Obama has also said that women should be free to make their own choices regarding late-term abortions, due to what he contends is their rarity and severity. In 2004, Obama called for the passage of the Ronald Reagan Biomedical Research Act, which would legalize embryonic stem cell research in Illinois.

Richardson

On his campaign Web site, New Mexico Gov. Bill Richardson stated, "As a Congressman, Cabinet Secretary, United Nations Ambassador and Governor, I have consistently supported women's reproductive rights. These difficult personal decisions should be kept out of the government's hands and rest with the woman, her family, her physician and her God." He has also stated, "I believe we can work together to make abortion safe, legal and rare."

Republicans

Brownback

In the first presidential debate in 2007, Sen. Sam Brownback said that the day Roe v. Wade was repealed, if ever, would be "a glorious day of human liberty and freedom." He is an opponent of Roe v. Wade and abortions and voted against a $100 million bill aimed at reducing unwanted, including teenage, pregnancy through education and contraceptives. Brownback does not support embryonic stem cell research, believing that adult stem cells are equally viable. He has consistently voted to ban late-term abortions.

Gilmore

In an address in 2001, former Virginia Gov. Jim Gilmore said, "When it comes to the most difficult decision a woman must make -- whether or not to have an abortion -- I believe she should be fully informed about the medical implications of that decision and have an opportunity to reflect on that information. That's why I support legislation to require informed consent and establish a 24-hour waiting period for abortion." In the GOP presidential debate at Reagan library in 2007, he said it would be a good day when Roe v. Wade is repealed, believing it was "wrongly decided." Despite these beliefs, Gilmore has also said that within the first eight to 12 weeks of pregnancy, abortion should be legal. His beliefs, he said in the debate, have "never changed."

Giuliani

In the 2007 GOP presidential primary debate, former New York City Mayor Giuliani stated that it would be "OK" to repeal Roe v. Wade, but added, "it would be OK also if a strict constructionist judge viewed it as precedent and I think a judge has to make that decision." He also said that states should make decisions on whether or not to fund abortion. Giuliani also said that embryonic stem cell research, if limited to existing embryos and used solely for non-cloning purposes, should be legal. Since the first debate, Giuliani has clarified his belief that a woman should have the final chopice as to whether or not to have an abortion.

Huckabee

Former Arkansas Gov. Mike Huckabee stated in the 2007 GOP debate that if Roe v. Wade were repealed, it would "most certainly" be a good day for America. Huckabee is against embryonic stem cell research, saying, "I don't think it's right to create a life to end a life." He has stated support for South Dakota's legislation outlawing all abortions, with exceptions only in cases where the mother's life is at stake, not for rape or incest. Huckabee has also stated that anti-abortion legislation must expand. "Life begins at conception but it doesn't end at birth. And if we're really pro-life we have to be concerned about more than just the gestation period," he said.

Hunter

California Rep. Duncan Hunter has a strong legislative record against abortion law. He voted in favor of a ban on late-term abortion. He stated at the GOP presidential debate in the Reagan library that repealing Roe v. Wade would be good for America, and later said that he would like to "show Mrs. Reagan the alternatives" to embryonic stem cell research, "which are adult stem cells." Hunter has voted against embryonic stem cell research.

McCain

Sen. John McCain of Arizona has said that he opposes abortion except in the cases of rape, incest, or danger to a mother's life. McCain's statements on Roe v. Wade's repeal, however, appear to have been at odds. In an Associated Press interview in 1999, McCain said, "I'd love to see a point where Roe v. Wade is irrelevant, and could be repealed because abortion is no longer necessary. But certainly in the short term, or even the long term, I would not support repeal of Roe v. Wade, which would then force women in America to (undergo) illegal and dangerous operations." However, in the GOP presidential debate at the Reagan library, McCain said he would support a repeal of the law. He voted to ban late-term abortions. McCain said he would support expanded stem cell research and, along with 57 other senators, signed a letter to the president urging him to do so.

Paul

A statement by the GOP Liberty Caucus, of which Texas Rep. Ron Paul was former chairman, stated that Paul was "very pro-life." He voted to ban late-term abortions and against embryonic stem cell research, which he said in the GOP primary debate was not "authorized under the Constitution." Paul did not, however, vote to ban human cloning for reproduction and medical research.

Romney

In the 2007 GOP debate, former Massachusetts Gov. Mitt Romney said it would "absolutely" be a good day for America if Roe v. Wade is repealed. However, Romney later stated that "I've always been personally pro-life, but for me, it was a great question about whether or not government should intrude in that decision. And when I ran for office, I said I'd protect the law as it was, which is effectively a pro-choice position." However, Romney says he has since changed his position: "Two years ago…the conclusion I reached was that cloning and creating new embryos was wrong, and that we should, therefore, allow our state to become a pro-life state."

Tancredo

Rep. Tom Tancredo of Colorado said in the GOP presidential primary debate, "After 40 million dead because we have aborted them in this country, (the day Roe v. Wade is repealed) would be the greatest day in this country's history." At the same debate, Tancredo called embryonic stem cell research "morally reprehensible in some ways" and has voted against it. He also voted to ban late-term abortions. On his Web site, Tancredo states, "As a devout Christian, father, and grandfather, I am a strong believer in the right to life for the unborn child."

Thompson

At the May 3 Republican debate in California, former Wisconsin Tommy Thompson said he would favor the repeal of Roe v. Wade. He signed one of the nation’s first laws banning late-term abortions. "I believe it should be left up to the states. That was what was originally implied, and the Constitution was changed when the Supreme Court made the decision. I have made a record of pro-life for a long time, signing the partial-birth abortion, pre-notification for parents and so on. I think it's an important imperative that states have the responsibility for making these laws."