'Socialist' Bernie Sanders enters US presidential race
Bernie Sanders, a US senator from Vermont who identifies as a socialist, is seeking the Democratic nomination for the presidency.
Mr Sanders joins Hillary Clinton in the Democratic primary race, where some say he could push her policies to the left.
Known for his progressive political agenda, Mr Sanders is a strong supporter of expanding social benefits and raising the minimum wage.
The Democratic National Committee said it welcomed his announcement.
"This country today, in my view, has more serious crisis than at any time since the great depression of the 1930s," he said. "For most Americans their reality is that they are working longer hours for lower wages."
Mr Sanders caucuses with Democrats, even though he was elected to congress without party affiliation.
He is running for the Democratic nomination, he says, because running as a third-party candidate would diminish his chances of winning the presidency.
Unlike other major candidates who announced their presidential ambitions at large rallies outside of Washington or over the internet, Mr Sanders made his announcement at a podium set up on the Capitol Building's north garden.
With no opening music or videos, Mr Sanders walked to the podium, made a short statement, and took several questions from gathered reporters.
Analysis - Anthony Zurcher, BBC News
So Hillary Clinton is going to have to beat someone if she wants to be the Democratic nominee for president.
"People should not underestimate me," Senator Bernie Sanders of Vermont told the Associated Press on Wednesday, but the reality is he doesn't stand much of a chance against the juggernaut that is Hillary, Inc.
The self-professed "democratic socialist" eschews big-time fundraising and is to the left of much of the Democratic primary electorate.
Still he's the kind of crusty, unvarnished liberal that some voters will find refreshing and can, at least, serve as a protest vehicle for those on the left who see Mrs Clinton as too moderate, too slick or too corporate.
It seems increasingly unlikely that the left-wing progressives will get their dream candidate, Massachusetts Senator Elizabeth Warren, so Mr Sanders may end up being their next best thing.
In 2010 in a procedural move known as a "filibuster", he railed against Wall Street and corporate greed on the Senate floor that was aimed at stalling a bill to extend tax cuts.
Sanders' identity as a socialist makes him a unique player in the American political arena, where the term "socialist" is often used pejoratively.
There have been widespread calls for Senator Elizabeth Warren of Massachusetts, who has a largely progressive political agenda, to throw her hat into the ring. She has said she will not run.
Sanders was elected to Congress as a member of the US House of Representatives in 1991, and previously served as the mayor of Burlington, Vermont.