Downing Street says Boris Johnson is "looking forward to working closely" with United States President-elect Joe Biden on standing up for a rules-based international system.
The Prime Minister offered his congratulations via Twitter at the weekend, after projections said Mr Biden had won the 2020 American election, but he has not yet spoken to him directly.
Mr Biden has begun preparations to move into the White House, including work on some key military decisions, which could have significant implications for the UK's Armed Forces.
From January, Mr Biden will be the most powerful person on the planet, commander-in-chief of the world’s most powerful military, leading the UK’s closest ally.
Defence Secretary Ben Wallace said: "We congratulate, the Government congratulates, the Vice President-elect Kamala Harris for her amazing achievement as the first woman, first black woman to be a vice president, and, indeed, the President-elect Joe Biden.
"We look forward to working with them. We’ve had a good relationship with Donald Trump but, you know, it's in our interest to all work together and I’m sure we will."
There are important military decisions for the incoming president to attend to, in which the UK has a big stake.
They include the direction of the military campaign against the so-called Islamic State terror group.
There is also Afghanistan, where the US is withdrawing troops, saying it will get them all out by April if the Taliban commits to peace talks and severs ties with Al Qaeda.
Donald Trump, meanwhile, suggested last month that remaining American service personnel in Afghanistan could leave the country by Christmas.
According to the US Inspector General, commitments by the Taliban have not yet met, and Britain’s Chief of Defence Staff, General Sir Nick Carter, says we must "keep the Taliban’s feet to the floor" on their approach to talks.
Dr Julie Norman, US Politics lecturer at University College London, told Forces News: "We know that Biden, like Trump, wants to reduce the number of US troops involved in Afghanistan in particular, also in Iraq, however, what we do expect under Biden is a very different style in terms of doing that.
"With Biden, we expect those decisions to be in conjunction with defence, with military personnel on the ground and also with allies, so we expect some reductions in troop numbers, but not a complete withdrawal."
The Prime Minister has offered his congratulation to the President-elect on social media, but will be well aware Mr Biden once described him as "a physical and emotional clone of President Trump".
Mr Biden has also expressed concern about the future of the Good Friday Agreement and Northern Ireland, because of Boris Johnson’s planned law which would change the Brexit agreement.
Dr Norman continued: "Biden is, at the end of the day, a pragmatist. The US-UK special relationship is special for a reason.
"It extends beyond just personal relationships and, in the long run, I don’t see this being damaging at all to the UK. There will still be a strong relationship between the US and the UK with Biden."
Mr Trump, who spent time on the golf course at the weekend, insists the election is not over and has said he plans to fight the result in the courts.
While millions of Americans are celebrating, it is worth noting that President Trump, even in defeat, got the second-highest vote in history in a presidential election.
The United States remains divided.
The President-elect believes healing is needed, both at home and abroad, including with the NATO alliance.
As Mr Biden plots his first days in the White House, his focus will inevitably be on home affairs, particularly the coronavirus pandemic and economic fallout.
However, his experience can tell him the entire world will be calling on him, not just the American people.