The inquiry is being cheered on by Donald Trump, who was twice impeached by the House - a historic first - when it was controlled by Democrats but acquitted by the Senate both times. Trump, the front-runner in the race for the Republican nomination to challenge Biden in next year's U.S. presidential election, has been charged in four separate criminal cases this year.
The White House dismisses the move as unsupported by evidence.
WHAT IS AN IMPEACHMENT INQUIRY?
The U.S. Constitution empowers Congress to impeach federal officials including the president for treason, bribery and "other high crimes and misdemeanors." A president can be removed from office if the House approves articles of impeachment by a simple majority and the Senate votes by a two-thirds majority to convict after holding a trial.
An impeachment inquiry is a formal step that can precede a House vote on whether to approve articles of impeachment and eventually a trial in the Senate.
The House in 2019 voted for an impeachment inquiry into Trump before his first impeachment charging him with abusing his power as president by pressuring Ukraine to investigate Hunter Biden's business dealings. It did not hold a full impeachment inquiry before bringing impeachment charges in the final weeks of Trump's presidency following the Jan. 6, 2021, Capitol attack.
Senate Republicans both times provided sufficient votes to acquit Trump.
WHAT ARE THE ALLEGATIONS?
Republicans allege that Biden's son Hunter has profited in business dealings with foreign entities by arranging access to then-Vice President Biden. They also allege that the president himself has profited.
Separately, they also say that the Justice Department interfered with investigations into Hunter Biden's taxes. U.S. Special Counsel David Weiss, who is leading that investigation, denies that charge.
WHAT DO DEMOCRATS SAY?
The White House has denied the charges. Democrats say the congressional probes are baseless and politically motivated, arguing they are a distraction from the four criminal indictments against Trump.
"Republicans' probe is a transparent effort to weaponize Congress to do Trump's bidding," Raskin said in a statement before McCarthy's announcement.
White House spokesperson Ian Sams dismissed the move as "extreme politics at its worst."
WHAT IS THE EVIDENCE?
Republicans have pointed to a U.S. government document in which an informant refers to the head of Burisma, a Ukrainian company for which Hunter Biden sat on the board of directors, saying: "it cost 5 (million) to pay one Biden, and 5 (million) to another Biden," referring to alleged payments to two members of the Biden family.
Devon Archer, an associate of Hunter Biden, said in an interview with congressional investigators in July that he was not aware of any such payments.
The Burisma head said he did not have any contact with Joe Biden or his staff, and that Biden did not help him or the company while he was vice president, according to a transcript of an interview released by Jamie Raskin, the top Democrat on the House Oversight Committee.
Archer also told congressional investigators that Hunter Biden put his father on the phone with foreign investors or associates "maybe 20 times" over the course of about 10 years.
Archer said Hunter Biden sought to create "an illusion of access to his father," but that those conversations did not involve any business dealings, and he was not aware of any wrongdoing by the elder Biden.
DOES THE HOUSE HAVE THE VOTES?
McCarthy was facing mounting pressure from hardline members of his party's right flank. Representative Matt Gaetz had suggested McCarthy's position as speaker was at risk if he did not support impeachment, while Representative Marjorie Taylor Greene had said she will not vote to fund the government without a vote on the impeachment inquiry.
McCarthy's decision to launch one without first calling a vote avoided a test of his narrow 222-212 majority, not all of whom supported the move.
WHAT WILL THE SENATE DO?
Under the Constitution, after the House votes to impeach an official, the Senate holds a trial. Removal of the official requires a two-thirds majority of the Senate.
Dick Durbin, the No. 2 Senate Democrat and head of its Judiciary Committee, has said that if the House votes to impeach Biden, the Senate would have no choice but to take it up.
The Senate is unlikely to convict Biden, where his Democratic Party holds the majority and some Republicans have said they have no appetite for an impeachment trial.
No president has been removed from office by the Senate following an impeachment.
WHAT OTHER LEGAL TROUBLES DOES HUNTER BIDEN FACE?
Weiss has said prosecutors will seek to indict Hunter Biden on tax and gun charges by Sept. 29. Investigators have been probing him since 2019.
Hunter Biden's lawyers had negotiated a plea deal that would have allowed him to plead guilty to not paying taxes on $1.5 million in income between 2017 and 2018 and entered into a separate deferred prosecution argument for illegally owning a firearm while using drugs, but the arrangement collapsed over the summer.
The criminal prosecution could mean Hunter Biden may face a trial while his father is campaigning for reelection.
(Reporting by Makini Brice; Editing by Scott Malone and Daniel Wallis)
