A longtime federal tax litigation attorney, Bachmann entered politics in 2000 as a Minnesota state senator. In 2006 she became the first female U.S. representative from Minnesota and in 2010 founded the Tea Party Caucus in Congress.

Romney, a management consultant, served as CEO of Bain & Company and then co-founded a spin-off investment firm, Bain Capital, that quickly made him a multimillionaire. In his first run at politics, Romney lost the 1994 Massachusetts U.S. Senate race to to incumbent Democrat Ted Kennedy. Romney was elected governor of Massachusetts in 2002 and did not seek re-election in 2006.

The longest-serving governor in Texas history is a former West Texas cotton farmer who started his political career as a Democrat in the Texas House. After switching to the Republican Party, Perry was elected agriculture commissioner, then lieutenant governor. He succeeded George W. Bush as governor in December 2000 and has since been re-elected three times.

Paul, 76, and his wife Carol have five children, all married with kids of their own. Paul's son, Rand, joined him in Congress in 2010 as a Republican senator from Kentucky.

Bachmann, 55, and her husband, Marcus, a clinical psychologist, have five biological children and have been foster parents to 23 teenage girls.

Romney, 64, and his wife, Ann, have five grown sons, all of whom have joined him on the campaign trail.

Perry, 61, married his childhood sweetheart, Anita, whom he met at age 8 at a piano recital. They have two children, Griffin and Sydney, and a daughter-in-law, Meredith.

Paul graduated from Gettysburg College with a degree in biology. He specialized in obstetrics/gynecology at the Duke University School of Medicine.

Bachmann graduated from Winona State University in Minnesota and received a degree in tax law from Virginia's College of William & Mary. Bachmann also received a law degree from Oral Roberts University in Oklahoma.

Romney has no military experience. He served as a Mormon missionary and was given a military deferment during the Vietnam War. He has said he longed to serve and regrets not having done so.

Paul was raised Lutheran but currently attends a conservative Baptist church. In an article titled "Christmas in Secular America," Paul wrote that "a rigid separation between church and state has no basis in either the text of the Constitution or the writings of our Founding Fathers."

The Romney family has practiced Mormonism since the former governor's great-great-grandparents joined the church in 1841 after meeting its founder, Joseph Smith. When he was 19, Romney went on a 30-month mission trip to France.

Raised as a Methodist, Perry now attends an evangelical church in Austin. At the 30,000-strong prayer rally he hosted in Houston in August, Perry told the crowd that God was the "only hope" for a nation in crisis.

Not applicable. Perry entered the presidential race in August, a month after the Federal Election Commission released the most recent campaign finance reports.

Not applicable. Perry entered the presidential race in August, a month after the Federal Election Commission released the most recent campaign finance reports.

Paul has said that "true conservatives and libertarians should understand that the solution to our moral and cultural decline does not lie in a strong centralized government."

As a constitutional conservative, Bachmann says she believes "in the founding fathers' vision of a limited government that trusts in and perceives the unlimited potential of you, the American people."

Romney has invoked the 10th Amendment to defend his health reform plan for Massachusetts, which some Republican opponents have compared to the federal reform they revile: “One thing I’d never do, by the way," Romney says, "is impose a one-size-fits-all policy on the nation.”

From his lawsuits challenging federal health care reform and environmental programs to his suggestions that Texans were so angry with Washington that they might consider secession, Perry has repeatedly invoked the 10th Amendment. He promises to "stop the federal intrusion upon states by runaway agencies like the EPA" and he wrote his book Fed Up! to "rally Americans to restore the proper, constitutional balance between the federal government and the states."

Cut taxes and spending, eliminate regulations imposed by the "job-killing" EPA and stop cap-and-trade practices. “There are over 600 American companies that have gone to Ireland because of the tax rate,” Bachmann said.

Paul opposes federal health care reform and believes the U.S. should encourage free-market competition by putting "pressure on the providers" and forcing them to lower their costs to remain in business. He also supports allowing tax deductions for all health care costs.

Romney believes states should implement their own health care plans, like Massachusetts did when he was governor. Though his state's individual mandate has drawn comparisons to "Obamacare," 98 percent of Massachusetts residents now have health insurance at a cost of $350 million a year, or 1 percent of the state budget.

Perry's first order of business would be to repeal "Obamacare," then "start over" by freeing states of federal mandates and giving local governments more control over Medicaid and other social programs. Texas has been good fodder for Democrats: It has country's highest rate of uninsured individuals.

Paul is "strongly pro-life" and has said abortion could lead the country toward legalizing euthanasia, but he believes legalization of the practice should be left to individual states, not to the federal government.

Bachmann and her husband, a psychiatrist, who staunchly oppose abortion rights, have repeatedly counseled women against having abortions. "We would take them in. We would drive them over to pro-life centers. ... It was a privilege to be a part of bringing new life into the world.”

Romney believes Roe v. Wade should be overturned so states can independently decide whether to outlaw abortion. He has angered some conservatives by not signing a pledge to appoint anti-abortion advocates to top federal positions. Romney campaigned in 1994 and 2002 as an abortion rights supporter but has since switched positions.

An ardent abortion opponent, Perry signed a pledge to use his federal power, if elected, to appoint anti-abortion advocates to top positions and to work to defund Planned Parenthood.

In 2007 Paul said he no longer believes in capital punishment because it "has been issued unjustly," even in cases with DNA evidence.

Bachmann's position on the death penalty is unclear. She has never had to vote on the matter or oversee an execution, and there is no capital punishment in Minnesota.

During Perry's tenure, 233 convicted criminals have been executed, more than any U.S. governor in modern history. He has commuted the death sentences of 31 inmates, including 28 who the U.S. Supreme Court said could no longer be executed because they were juveniles at the time of their crime.

Paul backed tax incentives for clean energy development but wants environmental disputes settled by the states or the courts. He has supported Arctic drilling to increase U.S. energy independence but has opposed tax incentives for oil and gas drilling.

It'll be lights out for the EPA if Bachmann is elected, as she has vowed to shut down the agency and end its environmental regulations. "The radical environmentalists have demanded that we lock up all our energy resources," she has said.

Romney says he believes the world is getting hotter but doesn't know "if it's mostly caused by humans." He opposes increasing regulations on emissions. "What I'm not willing to do is spend trillions of dollars on something I don't know the answer to," he has said.

Texas currently has seven lawsuits filed against the EPA challenging regulations that limit emissions of greenhouse gases and other pollutants. In his book Fed Up!, Perry calls global warming “one contrived phony mess."

Paul voted in favor of building a border fence to keep out immigrants from Mexico and has proposed a constitutional amendment to remove birthright citizenship. In 2007 Paul said he sees the "immigration problem as a consequence of our welfare state."

Although she advocated to bring orphaned children to the U.S. after the 2010 earthquake in Haiti, Bachmann strongly opposes illegal immigration.

Romney has said the U.S. ought to build a border fence, outlaw "sanctuary cities" and keep employers from hiring illegal immigrants. He's in favor of creating an employment-verification system.

Perry made outlawing "sanctuary cities" a priority during the last legislative session. He has increased funding for border security in Texas and recently asked the federal government to reimburse Texas for the cost of imprisoning illegal aliens.

Bachmann supports teaching intelligent design in schools. She says curriculum should be set at the local level, because government shouldn't decide on a scientific issue "when there is reasonable doubt on both sides."

Romney has said he believes God created the universe and that “evolution is most likely the process he used to create the human body.”

Perry says evolution is a theory "with some gaps." On the campaign trail, he inaccurately told a child that "in Texas, we teach both creationism and evolution in our public schools. Because I figure you’re smart enough to figure out which one is right.”

Same Sex Marriage

Rick Perry Perry has backtracked on a claim made in his book Fed Up! that states should decide whether to sanction same-sex marriage. He now says he supports a constitutional amendment to prohibit same-sex marriage. "Obviously gay marriage is not fine with me. My stance hasn't changed. I believe marriage is a union between one man and one woman," he said.

Mitt Romney Although same-sex marriage is legal in Massachusetts, Romney signed a pledge to appoint officials, particularly judges, who oppose same-sex marriage. He has said he would defend the Defense of Marriage Act and has signed a pledge to support a constitutional amendment banning gay marriage.

Michele Bachmann Although Minnesota has a law on the books banning same-sex marriage, Bachmann proposed a state constitutional amendment in 2003 to prohibit it. She characterized homosexuality as "part of Satan" in a speech reposted by CBS. "Any of you who have members of your family that are in the lifestyle — we have a member of our family that is — this is not funny. It's a very sad life."