Sonia Sotomayor has stated her case for a place on the US Supreme Court to the Senate, saying her judicial philosophy is "fidelity to the law".
The nominee said during her 17 years as a federal judge she had sought to serve the interests of "impartial justice".
Ms Sotomayor - nominated by President Barack Obama - will be the first Hispanic to serve on the court if she is, as expected, confirmed in the post.
Some Republican senators want her to explain past rulings and comments.
These include her remark that a "wise Latina" could reach better legal conclusions than a white man.
Ms Sotomayor, 55, told the Senate Judiciary Committee that her personal story - of growing up in a poor New York neighbourhood to Puerto Rican parents, going to law school and rising to become an appeals court judge - was "uniquely American".
She paid tribute to her mother - sat behind her in the hearing - who she said had instilled in her the values of working hard and getting a good education.
RISE OF SONIA SOTOMAYOR
1954: Born in South Bronx to Puerto Rican parents
Father died when she was aged nine and her mother raised her
1979: Graduates from Yale and serves as an assistant district attorney in New York County
1984: Moves into private practice, specialising in intellectual property
1991: George Bush Snr chooses her as a district judge
1997: Bill Clinton nominates her to the circuit court
And she spoke of her experiences - big city prosecutor, corporate litigator, trial and appelate judge.
Seeking to counter criticism from Republicans that her personal or political views would influence her decisions, Judge Sotomayor said her judicial philosophy is simple: "Fidelity to the law".
"The task of a judge is not to make law - it is to apply the law," she said.
Senators are expected to begin questioning her on Tuesday in an attempt to find out more about her legal thinking. Both sides will also call witnesses.
In particular, they are likely to ask about one case in which she ruled that white firefighters in Connecticut had not been unfairly denied promotions.
The Supreme Court last month overturned that decision, ruling by five votes to four that the firefighters had been unfairly discriminated against.
Confirmation hearings for a new Supreme Court justice provide one of Washington's most imposing pieces of political theatre, correspondents say.
The hearings began with opening comments by the 12 Democratic and seven Republican senators.
Sen Patrick Leahy who chairs the committee and is a supporter of Ms Sotomayor, described her as "committed to the law" and "not to ideology".
"She has been a judge for all Americans. She will be a justice for all Americans," he said.
"Let no-one demean this extraordinary woman."
Sen Lindsey Graham told Judge Sotomayor: "Unless you have a complete meltdown, you're going to get confirmed."
He quickly added: "And I don't think you will [have a meltdown]."
Some of Ms Sotomayor's remarks have provoked controversy, in particular in 2001 when she said: "I would hope a wise Latina woman with the richness of her experiences would more often than not reach a better conclusion than a white male who hasn't lived that life."
Such comments, her critics say, suggest her decisions would stem from bias, empathy and emotion rather than strict interpretation of the law.
'Wise Latina': Ms Sotomayor said a wise Latina could reach a better conclusion than a white male
Discrimination: Her ruling that white Connecticut firefighters were not discriminated against was overturned by the Supreme Court
Empathy: President Obama said he wanted someone with empathy on the court, but critics say empathy has no place in law
Sen Jeff Sessions, the senior Republican on the judiciary committee, said: "I will not vote for, and no senator should vote for, an individual nominated by any president who is not fully committed to fairness and impartiality."
Fellow Republican Charles Grassley, senator for Iowa, said Mr Obama had nominated Judge Sotomayor for the wrong reasons.
"President Obama's empathy standard appears to encourage judges to make use of their personal politics, feelings and preferences.
"This is contrary to what most of us understand to be the role of the judiciary."
Ms Sotomayor is expected to win confirmation to the nine-member Supreme Court that rules on key political and social issues, and is the final arbiter of the US constitution.
But as she would replace Justice David Souter, another liberal justice, the balance of the conservative-leaning court would not be significantly altered.
She would, however, be not only the first Hispanic justice but only the third woman in the history of the court.
The hearing was briefly disrupted by shouts from two anti-abortion protesters, who were removed from the room.
Other anti-abortion protesters rallied outside the building.
US MEDIA REACTION TO THE SOTOMAYOR HEARING
Republican Senators have been very respectful and tried to walk a very thin tightrope. So far, they are doing a good job of it. But their principal theme looks like it's going to be worries about her racial bias, which is certainly very dangerous territory.
Judge Sotomayor followed her short, White House mandated script, and even forcefully did her best John Roberts imitation, saying that her "judicial philosophy" is "simple": "fidelity... to... the... law."Great, Judge... now we just need to hear how we reconcile that with "choosing to see" the facts you like in a case before you, and how it squares with the law you're supposed to be faithful to being so indefinite that a judge herself has to invent its meaning.
The Republican battle lines against Sotomayor have been drawn, with Senator after Senator weaving together President Obama's remarks about empathy and certain snippets of Judge Sotomayor's speeches, to assert that Judge Sotomayor will be biased, will not obey her judicial oath, or will let feelings dictate her judicial decision-making. Democratic Senators have pushed back on this by noting that the best proof of Judge Sotomayor's approach to judging is her judicial record, which is long, distinguished, and reveals a fair and careful judge.
The question emerging from Sotomayor's opening statement is whether Republicans will press the judge to explain exactly what she means by "law" and "the rule of law," and, relatedly, just how she goes about interpreting the Constitution and laws of Congress. If Republicans fail to do this, there will be little point to this proceeding.
Unfortunately, at the beginning of the Sotomayor hearing this morning, Republicans and Democratic senators framed the debate about Sotomayor's judicial philosophy in a caricatured way that seems unlikely to reveal the nuances of the kind of justice she will become: Republicans painted her as someone driven entirely by empathy and personal experiences and Democrats as a cautious moderate ruled entirely by previous precedents. Once the questioning begins, perhaps both sides will abandon these caricatures and press the more subtle questions that will define Sotomayor's tenure on the Court.
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