1st District - One to watch
Seat: Open with Rep. Bart Stupak's retirement
Why it's important: Democrat Stupak has held the seat in a district that leans Republican. If voters pick the GOP nominee in the fall, it could repaint a district Stupak has kept blue since 1992 back to red for a long time.
Strongest Republican candidates are surgeon Dan Benishek of Crystal Falls and two-term state Sen. Jason Allen of Alanson.
Who's also running: Democrat: Hay farmer and state Rep. Gary McDowell of Rudyard
Other Republicans: Retired autoworker Pat Donlon; attorney Linda Goldthorpe of McMillan; trucker Don Hooper of Iron River; steel sales representative Tom Stillings of Eastport
Independent: Businessman Glenn Wilson
Behind the ballot: Stupak's anti-abortion, pro-gun positions helped him keep hold of this district. Democrats hope McDowell, a Stupak look-alike on those key issues to this district, can neutralize what might otherwise have given the Republicans an edge in this conservative district.
2nd District - One to watch
Seat: Open with Rep. Pete Hoekstra's retirement
Why it's important: Because this district is solidly Republican, the likely GOP victor may hold this House seat for a long time. But the winner will still be a freshman, meaning a loss of clout for the state since Hoekstra is a nine-termer.
Hoekstra hasn't endorsed.
Republican candidates who have plenty of money to compete in this free-for-all are former state representative and businessman Bill Huizenga of Zeeland, who once served as Hoekstra's district director; former U-M and pro football player Jay Riemersma; two-term state Sen. Wayne Kuipers; and businessman Bill Cooper of Fruitport.
Who's also running: Other Republicans: Chris Larson of Ferrysburg; Field Reichardt of Grand Haven; and Ted Schendel of Honor
Democrats: Lake County Commissioner Nicolette McClure of Idlewild and Hope College history professor Fred Johnson of Holland
Behind the ballot: Riemersma is trying to capitalize on his football past in TV ads and his "Jay's playbook," a game plan for what he'd do in Congress. Riemersma played at the University of Michigan before going on to the Buffalo Bills and the Pittsburgh Steelers.
3rd District - One to watch
Seat: Open with Rep. Vern Ehlers' retirement
Why it's important: This usual Republican stronghold is Jerry Ford's old congressional seat, but the Democrats are given a shot at taking it this year.
Strongest Republican candidates are state Rep. Justin Amash of Cascade Charter Township, state Sen. Bill Hardiman of Kentwood, and business and health attorney Steve Heacock of Cascade Township.
Strongest Democrat is Pat Miles, a third-generation Grand Rapids resident, Harvard Law graduate and business lawyer.
Who's running: Grand Rapids attorney Louise Johnson and veteran Bob Overbeek of Wyoming, who served as an Air Force officer in Afghanistan, in the GOP primary
Democrat: former Kent County Commissioner Paul Mayhue
Behind the ballot: The district has been represented by a moderate Republican. But a strong Democratic candidate like Miles could have a chance in November if he can turn out the Democratic vote.
Seat: Rep. Dave Camp, R-Midland, is seeking his 11th term and is expected to win handily in the general election in November.
Top contender: Democrat Jerry Campbell
Seat: Rep. Dale Kildee, D-Flint, is seeking his 18th term and is expected to have an easy victory Tuesday and in November.
Top contender: Democratic challenger Scott Withers is in the primary. On the Republican side are John Kupiec and Rick Wilson.
Seat: Rep. Fred Upton, R-St. Joseph, is the longest-serving Republican in the delegation, having been first elected in 1986.
Top contender: Jack Hoogendyk, a former state representative from Kalamazoo, is challenging Upton from the right. The Democrat is longtime Kalamazoo City Commissioner Don Cooney.
Behind the ballot: The moderate Upton has survived challenges from the right before, and he heads into the primary with 30 times more cash to get out his message than Hoogendyk.
7th District - One to watch
Seat: Held by freshman Rep. Mark Schauer, who won in 2008 with less than 50 percent of the vote
Why it's important: After six-term Republican Rep. Nick Smith decided not to run again in 2004, this Republican-tilted district hasn't found a comfortable replacement, instead electing three new congressmen. Because of the seniority system in Congress, the turnover hasn't been helpful to the district or the state. Schauer hopes to break the freshman jinx.
Tim Walberg, R-Tipton, represented the district for one term before being ousted by Schauer in 2008. But he's in a GOP primary dog fight with attorney Brian Rooney of Dexter, a veteran whose family owns the Pittsburgh Steelers. Schauer has been able to sit back and watch the fireworks -- while sitting on his near-$1.7 million war chest.
Who's also running: Property developer Marvin Carlson of Manchester
Behind the ballot: Having a track record in business of creating jobs -- not just promising to pass business-friendly policies -- became a hot issue when Carlson, a successful real estate developer, challenged his rivals to publicly disclose their tax returns. Schauer and Walberg did; Rooney didn't. While the challenge didn't give Carlson a big boost, it put a spotlight on candidates' experiences in the business world.
Seat: Rep. Mike Rogers, R-Brighton, is finishing his fifth term.
Behind the ballot: In November, he'll face Democrat Kande Ngalamulume, a business analyst whose family emigrated from Zaire when he was a child, and Rogers is expected to win another term.
9th District - One to watch
Seat: Held by freshman Rep. Gary Peters, D-Bloomfield Township, who ousted longtime Republican Congressman Joe Knollenberg in 2008
Why it's important: This Oakland County district leans Democratic. But Peters is expected to have a serious race on his hands in the fall, partly because of voter anger over Washington spending and the high motivation of Republicans to vote.
The top contenders in the GOP primary are veteran Rocky Raczkowski of Farmington Hills and consultant Paul Welday of Farmington.
Who's also running: Also in the GOP primary are beauty consultant Anna Janek and former Oakland County Circuit Judge Richard Kuhn, but they lack campaign cash to wage big campaigns in the media-expensive district.
Behind the ballot: To get a sense of how heated the GOP primary has become, take a peek at the websites of Welday and Raczkowski to see their rebuttals to mud balls hurled at them. Welday titles his area, "Fight the Smears"; Raczkowski calls his long rebuttal section "Fact or Fiction."
Seat: Rep. Candice Miller, R-Harrison Township, who is seeking her fifth term.
Top contender: Her Democratic challenger in the fall is firefighter Henry Yanez of Sterling Heights.
Seat: Rep. Thaddeus McCotter, R-Livonia, is running for his fifth term.
Top contender: His Democratic challenger in the fall is former public school teacher Natalie Mosher of Canton Township, one of the few women running for a congressional seat in Michigan.
Seat: Rep. Sander Levin, D-Royal Oak, is running for his 15th term as the state's most powerful player in the House: He's the House Ways and Means Committee chairman.
Top contender: Self-described "underdog" Democratic state Sen. Mickey Switalski of Roseville is running against Levin in the primary.
The Republican is health insurance agent Don Volaric.
13th District - One to watch
Seat: Held by seven-term Rep. Carolyn Cheeks Kilpatrick, D-Detroit
Why it's important: Kilpatrick emphasizes her influential post on the House Appropriations Committee, which allows her to push for earmarks for the area, and downplays the legal problems of her son, jailed former Detroit Mayor Kwame Kilpatrick.
The district is solidly Democratic, so the winner of the Democratic primary should coast easily to victory in November.
Democratic state Sen. Hansen Clarke of Detroit zoomed ahead of other Kilpatrick challengers, and two recent polls said he'd beat the incumbent.
Who's also running: The big Democratic field includes businessman John Broad, Vincent Brown, Stephen Hume and Glenn Plummer. The Republican is John Hauler.
Behind the ballot: Kilpatrick felt the backlash of her son's legal troubles back in 2008, when she barely eked out a win in a three-way Democratic primary.
Seat: Held by Rep. John Conyers, D-Detroit, who chairs the House Judiciary Committee
Top contenders: Two Republicans are vying for the chance to take Conyers on: Pauline Montie of Southgate, who runs an auto parts business with her husband, and consultant Don Ukrainec of Trenton.
Seat: Held by Rep. John Dingell, D-Dearborn, the longest serving member ever in the House
Top contenders: Four Republicans are battling to take Dingell on: cardiologist Rob Steele of Ann Arbor; eighth-grade history teacher Tony Amorose of Dearborn Heights; John Lynch of Ypsilanti; and attorney Majed Moughni of Dearborn.