Mr Biden and Ms Harris were sworn in at noon Wednesday in front of the US Capitol in Washington DC, before a sparser audience than previous years due to the Covid pandemic.
More than 25,000 troops are also on patrol in the streets of the capital following the insurrection by a pro-Trump mob earlier this month.
You can watch Wednesday’s inauguration live, at the top of this page.
Lady Gaga performed the national anthem and Jennifer Lopez will provide a musical performance.
Mr Biden and the new first family walked into the White House hours after the inauguration, and Mr Biden was soon at work in the Oval Office.
He immediately signed his first executive orders to reverse many of Donald Trump’s previous policies.
These included a federal Covid mask mandate, a return to the Paris Agreement, and an end to the Muslim travel ban.
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