United States President Joe Biden moved quickly on his first day in office to address his country's four "converging crises" of the pandemic, the economic downturn it caused, climate change and racial injustice, signing 17 executive orders that marked a drastic departure from his predecessor Donald Trump's policies.
Mr Biden moved to rejoin the World Health Organisation (WHO) and Paris climate agreement, which the Trump administration had withdrawn from.
"The United States will continue to be a full participant and a global leader in confronting such threats and advancing global health and health security," Mr Biden wrote in a letter to United Nations Secretary-General Antonio Guterres.
"With the state of the nation today, there is no time to waste," Mr Biden said in the Oval Office following a scaled-down inauguration parade in Washington after he took his oath of office at the Capitol.
Wednesday's executive actions were just starting points, said Mr Biden, who acknowledged that legislation would also be needed for a lot of his policies.
Combating the coronavirus pandemic was at the top of his agenda.
Mr Biden signed an order requiring masks to be worn on federal property, and directed agencies to provide relief to Americans hit by the pandemic by extending pauses on evictions, foreclosures and federal student loan payments.
He also officially appointed a Covid-19 response coordinator to create a unified national response to the pandemic, and re-established the national security team responsible for global health security and biodefence.
He will also issue a new national strategy to tackle the coronavirus crisis and sign additional executive orders to boost testing, speed up vaccine distribution and better equip states to deal with Covid-19.
The US will join the WHO's efforts to distribute vaccines to low-income countries, Mr Biden's chief medical adviser Anthony Fauci told the WHO yesterday.
The US will also "fulfil its financial obligations" to the WHO, Dr Fauci said, reversing Mr Trump's brake on America's funding to the WHO.
President Joe Biden signed 17 executive orders, memorandums and proclamations hours after his inauguration. Here is a look at some of the key measures.
ON THE PANDEMIC
• Appointing Mr Jeffrey Zients as the official Covid-19 response coordinator who will report to the President to "aggressively" gear up the nation's response to the pandemic.
• Reinstating ties with the World Health Organisation.
• Bolstering the Deferred Action for Childhood Arrivals programme that protects from deportation immigrants brought to the United States as children, often called Dreamers.
• Ending the so-called Muslim ban that blocked travel to the US from several predominantly Muslim and African countries.
• Stopping construction of Mr Donald Trump's border wall with Mexico.
ON CLIMATE CHANGE
• Getting the US to officially rejoin the Paris climate accord 30 days from Inauguration Day on Wednesday.
ON RACIAL EQUALITY
• Designating Dr Susan Rice, Domestic Policy Council head, as leader of a "robust, inter-agency" effort requiring all federal agencies to make "rooting out systemic racism" central to their work.
ON THE ECONOMY
• Extending a federal moratorium on evictions.
• Continuing a pause on federal student loan interest and principal payments until the end of September.
Though he will focus primarily on domestic issues in his first days in office, the President has said that tackling the pandemic and climate change, in particular, will require global cooperation.
His first phone calls with foreign leaders will be with allies and partners, said White House press secretary Jen Psaki, adding that Canadian Prime Minister Justin Trudeau is first in line today.
Mr Biden moved to strengthen environmental protections, including cancelling the permit for the Keystone XL pipeline that would have transported crude oil from Canada to the US.
On immigration, he signed orders to halt construction of the US-Mexico border wall and to reverse Mr Trump's travel ban on Muslim-majority countries.
The new administration will also pause some deportations for 100 days to ensure "fair and effective immigration enforcement" and focus on US-Mexico border security, the Department of Homeland Security said in a memo on Wednesday.
Mr Biden also sent an immigration reform Bill to Congress, titled US Citizenship Act of 2021, that would provide undocumented immigrants who have lived in the US for a long time with an eight-year path to citizenship.
The White House also appointed career public servants to temporarily lead their agencies while Mr Biden's picks await Senate confirmation. Director of National Intelligence Avril Haines became the first of Mr Biden's Cabinet-level nominees to be confirmed by the Senate, by a vote of 84 to 10, on Wednesday.
Democrats now have de facto control of the Senate for the first time in a decade, after Vice-President Kamala Harris swore in three new Democratic senators on Wednesday. They were her successor Alex Padilla, who was appointed to fill the California seat she vacated after winning the 2020 election, and Georgia Democrats Raphael Warnock and Jon Ossoff, who won their run-off races earlier this month.
Republicans and Democrats now have 50 senators each, but Ms Harris, who is president of the Senate, will get to cast the deciding vote in case of any ties.