-year term in 2014. Here's how some people are reacting to the Michigan Democrat's decision:
"If you've ever worn the uniform, worked a shift on an assembly line, or sacrificed to make ends meet, then you've had a voice and a vote in Sen. Carl Levin. No one has worked harder to bring manufacturing jobs back to our shores, close unfair tax loopholes, and ensure that everyone plays by the same set of rules." — President Barack Obama
"Words cannot describe the value of Carl Levin's service to our state and to our country. Carl is respected by our colleagues in both parties because he has always been more concerned with getting the right answer and doing the right thing, rather than earning accolades for himself or engaging in partisan fights. His honor and his integrity are absolutely unmatched. The more people we have like Carl Levin serving in public office, the better off our country will be." — U.S. Sen. Debbie Stabenow, D-Mich.
"For more than 30 years, Carl Levin has been a thoughtful, compassionate voice in Washington. He effectively brought the needs and concerns of Michiganders to the halls of the Capitol. His service on behalf of Michigan and America is commendable. On behalf of our entire state, I applaud Sen. Levin for his dedication and wish him a healthy, fulfilling retirement." — Michigan Gov. Rick Snyder, Republican
"The retirement of my good friend Carl Levin is a terrible loss to our state. Carl is a giant, and he and his service have been of enormous value to the people of Michigan and this Nation. I wish this giant a long retirement, full of well-earned joy and contentment with his wonderful wife Barbara and family." — U.S. Rep. John Dingell, D-Mich.
"Michigan voters have been able to rely on Carl Levin with total confidence. They knew his motives were their welfare, his values were unimpeachable, and his work ethic was a model for all of us. He's been our champion, our lion, our conscience. Personally, he's been a friend and a hero from long before I even considered politics." — former Michigan Gov. Jennifer Granholm, Democrat.
"Carl Levin has had a distinguished and honorable career in the United States Senate. I thank him for his years of dedicated service to the citizens of Michigan and wish him all the best in his future endeavors." — Michigan Attorney General Bill Schuette, Republican
"Sen. Levin has been a model public servant and a valued member of the Senate for more than thirty years. I'm particularly thankful for his leadership on behalf of our men and women in uniform. I am confident that we will recruit a great Democratic leader who will continue to fight for the values and priorities Sen. Levin advocated for all these years. We fully expect to keep Michigan blue in November 2014." — Sen. Michael Bennet of Colorado, chairman, Democratic Senatorial Campaign Committee
"Over the last few months, the 2014 map has gone from sorta difficult to really tough for Senate Democrats. Politically, Sen. Levin's decision knocks a Democratic Senate already on defense far back on their heels and offers us a real pick up opportunity. Republicans can win in Michigan, as the governor, lieutenant governor, secretary of state, and attorney general have proven. That is why we've been speaking to local officials and grassroots organizations in preparation for Sen. Levin's potential retirement, and now that groundwork will start to pay off." — Brad Dayspring, communications director, National Republican Senatorial Committee