After nearly seven decades at his wife's side, Prince Philip died on April 9 last year.
He was just two months shy of his 100th birthday.
Today's memorial service will be very different from the funeral that took place at Windsor Castle's St George's Chapel.
Poignant photos showed Queen Elizabeth sitting by herself during the service, as Covid rules at the time meant she and the 29 other mourners allowed to attend had to sit separately.
But the memorial at Westminster Abbey will be a much larger affair with no restrictions on the number able to attend.
The occasion will mark the Queen's first public event in five months after illness left her advised to rest.
Senior royals and European royals, and foreign dignitaries will all be in attendance.
U.K. Prime Minister Boris Johnson, military figures and more than 500 representatives from charities and organisations championed by Prince Philip have also been invited.