CHRIS COONS, DEMOCRAT
He has been chief executive of Delaware's largest county since 2004, having previously served four years as county council president.
Coons was born in Greenwich, Conn., and moved to Delaware as a child. After his parents divorced, his mother married into the family that founded and runs the privately held W.L. Gore & Associates, maker of Gore-Tex fabrics and other products. Before becoming county executive, he was a lawyer for Gore.
He became a Democrat in college following a trip to Africa that caused him to question his Republican beliefs. He wrote of the experience in a college newspaper column, which political opponents seized upon this year because of its title: "Chris Coons: The Making of a Bearded Marxist."
Coons, 47, is married and has three children. He hold degrees in political science and chemistry from Amherst College and graduate degrees in religion and law from Yale University.
MARCO RUBIO, REPUBLICAN
An attorney, the 39-year-old Miami native served as speaker of the Florida House and became a rising star in the GOP as a fiscal conservative.
Born to Cuban immigrants, Rubio began his career in public service as a city commissioner in West Miami and entered the Florida House at age 29. Within eight years he ascended from a representative seated by special election to majority whip, majority leader and eventually House speaker.
Fiscal conservatism is the cornerstone of Rubio's philosophy. He says controlling the national debt and paring government entitlement programs are the most important things lawmakers can accomplish. Rubio wants to reinstate tax cuts for the wealthy enacted under President George W. Bush in 2001 and 2003, slash corporate taxes and eliminate taxes on capital gains and dividend profits. He also supports eliminating the estate tax.
In the Republican primary for the Senate, Rubio initially trailed Gov. Charlie Crist by 30 points. The national GOP quickly embraced Crist, but Rubio overtook him with substantial tea party support. Twice he set records for the most lucrative three-month fundraising periods for a Senate race in Florida, collecting $4.5 million and $5 million, respectively. Crist, meanwhile, turned to a bid as an independent.
Rubio lives in West Miami with his wife, Jeanette, and four children.
RAND PAUL, REPUBLICAN
The 47-year-old eye doctor tapped into tea party fervor with a fiercely antiestablishment message. He has strong family ties to politics -- his father is Republican Rep. Ron Paul of Texas, a former presidential candidate and libertarian icon.
Quiet and intense, Rand Paul railed against government bailouts and deficit spending in promoting low taxes and limited government. He's also personally frugal, according to friends who say he mows the lawn at his home in a gated community and shops the Internet for cheap golf shoes.
Paul was born in Pennsylvania, grew up in Texas and settled in Bowling Green, a college town near his wife's hometown, about 20 years ago. He runs his own ophthalmology practice.
Paul attended Baylor University but left early without a bachelor's degree for medical school at Duke University. He helped create a certification group for ophthalmologists after objecting to a powerful medical group's policy.
Paul and his wife, Kelley, have three sons. He has coached youth baseball, soccer and basketball, and his family attends a Presbyterian church, where his wife is a deacon.
ROB PORTMAN, REPUBLICAN
Soft-spoken and meticulous, he is known for his deep knowledge of tax and finance issues and has taught college courses on the subject. The former congressman was also closely allied with both Bush administrations.
Born in Cincinnati in 1955, he graduated from Dartmouth College and the University of Michigan law school.
Under President George H.W. Bush, Portman's roles ranged from White House staffer to legislative liaison to stand-in at political debate rehearsals. When George W. Bush entered the White House in 2000, Portman was named budget director and later U.S. trade representative.
He represented southwest Ohio in Congress for 12 years beginning in 1993. As a congressman, he championed bills that streamlined the federal tax code, increased IRS oversight, provided financial incentives to countries that protect their rainforests and allowed display of the Ten Commandments in public places.
He owns the historic Golden Lamb Inn in Lebanon, Ohio, the state's oldest continuously operating business. An advocate for restoration, he wrote a book about the hotel's history called "Wisdom's Paradise." He and his wife, Jane, have three children.
KELLY AYOTTE, REPUBLICAN
She resigned as attorney general to run for the Senate. After former Alaska Gov. Sarah Palin endorsed her, she won the party primary by 1,667 votes over a conservative supported by local tea party activists.
A fiscal and social conservative, Ayotte, 42, opposes gay marriage and abortion. She pledges not to ask for special spending requests known as earmarks, something retiring GOP Sen. Judd Gregg believed was a legitimate way to direct money to worthy projects.
Ayotte also wants federal agencies to propose 20 percent cuts to their budgets to start a discussion about what funding is essential. She supports repealing the health care law and opposes economic stimulus spending. She says the private sector should handle health care reforms and creating jobs, not government.
She would not raise the retirement age for Social Security for those near retirement but would consider it for younger workers. She opposes reinstating the inheritance tax.
DAN COATS, REPUBLICAN
This new face is not quite as fresh as others. Coats served in the Senate from 1989 to 1999.
He was born in Jackson, Mich., and earned a law degree from Indiana University in 1971. He joined Rep. Dan Quayle's staff in 1976 and won Quayle's House seat when Quayle ran for the Senate in 1980. When Quayle was elected vice president in 1988, Coats was appointed to fill his Senate seat, and he developed a reputation as a social conservative.
He served as U.S. ambassador to Germany from 2001 to 2005 and worked as a Washington lobbyist before deciding to take another run at Senate, saying he didn't like where the country was headed.
Supporters say Coats has integrity, experience and a conservative record well-suited for Indiana. Critics say he's a rich Washington insider who has lived away from the Hoosier state for too long.
Coats, 67, and his wife, Marsha, have three children.