The former president’s casket has been set down at the front of the National Cathedral.
The choir leads the mourners in singing the hymn Praise, My Soul, the King of Heaven.
After a prayer from Reverend Randolph Marshall Hollerith, Bush Sr’s granddaughters Lauren Bush Lauren and Ashley Walker Bush will begin the first reading.
US and world leaders and dignitaries are at the US National Cathedral in Washington DC to pay their respects at the state funeral of former President George HW Bush.
The body of Mr Bush, which had been lying in state at the US Capitol, was moved to the cathedral just before the funeral began.
His son, ex-President George W Bush, is to deliver one of the eulogies.
Mr Bush senior, who served as the 41st US president between 1989 and 1993, died on Friday at the age of 94.
He will be buried in his home state of Texas, alongside his wife Barbara.