Cameron takes oath in Commons
David Cameron has taken the oath and retaken his Commons seat as Prime Minister at the head of a majority Conservative government.
The MP for Witney chose to swear - rather than affirm - on a King James Bible.
He followed Speaker John Bercow and Father of the House Sir Gerald Kaufman, the Labour MP for Manchester Gorton.
The beginning of the swearing in process followed a second Royal Commission in as many days, summoning MPs to the House of Lords to hear the Queen's consent for Mr Bercow continuing as Speaker.
All MPs are expected to be sworn in before the State Opening of Parliament next Wednesday.
Mr Cameron said: "I swear by almighty God that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth, her heirs and successors according to law, so help me God."
Mr Bercow chose to affirm his oath after reporting to MPs on the Royal Commission.
He told the Commons: "Her Majesty by her Royal Commissioners has been pleased to approve the choice made of myself for the office of Speaker.
"I have in your name and your behalf made claim by humble petition to Her Majesty to all your ancient and undoubted rights and privileges.
"Particularly to freedom of speech in debate, freedom from arrest and freedom of access to Her Majesty whenever occasion shall require, and that the most favourable construction shall be put upon all proceedings.
"All these Her Majesty by her commissioners has been pleased to confirm in as ample a manner as they have ever been granted or confirmed by herself or by any of her Royal predecessors."
In the background to the pageantry of a state occasion, a turf war continued on the Opposition benches.
SNP MP Pete Wishart, one of the six nationalist MPs joined by 50 new colleagues in this Parliament, sat on the Labour front bench, behind the Despatch Box and next to senior figures such as Hilary Benn, the shadow foreign secretary, and Rose Winterton, the Labour chief whip.
For a while, he was joined on the front bench by Michelle Thomson, SNP MP for Edinburgh West, but she moved back to the second row - still normally a Labour-only bench - after exchanging words with the principal doorkeeper Robin Fell.
Swearing in of MPs will continue today, tomorrow, Thursday and next Tuesday.
Acting Labour leader Harriet Harman opted to affirm as she led the Opposition in the formalities.
Leadership contenders Yvette Cooper and Liz Kendall were also among those to undertake the process today.
Former Liberal Democrat leader Nick Clegg also made an appearance and stood alongside his fellow party member Alistair Carmichael, who previously held the post of Scottish Secretary.
Mr Clegg chatted to the SNP's Alex Salmond, the former First Minister of Scotland, while he waited in line.
Former Labour leader Ed Miliband, fresh from a post election holiday, took the oath to return to the green benches.
Mr Miliband appeared to skip the queue to join Mr Clegg in conversation as the two former leaders joined the backbench ranks.
Senior SNP MPs, including Mr Salmond and Angus Robertson, swore in.
Their 50 new colleagues will begin joining them tomorrow when 2015 MPs take their turn in the queue.
Labour veteran Dennis Skinner, MP for Bolsover, was barely audible and almost mumbled as he took his turn and chose to affirm.
Later on Ukip's only MP in the Commons, Douglas Carswell, MP for Clacton chose to swear on a King James Bible.
Plaid Cymru's new Parliamentary group leader Jonathan Edwards, MP for Carmarthen East and Dinefwr lined up alongside fellow Plaid Cymru MPs Liz Saville- Roberts (MP for Dwyfor Meirionnydd) and Hywel Williams (Arfon).
The SNP's Angus MacNeil swore his oath in both English and Gaelic.
A clutch of 2015 MPs defied official expectations to take the oath.
They included Tories Johnny Mercer (Plymouth Moor View), Anne-Marie Trevelyan (Berwick-Upon-Tweed) and Michael Tomlinson (Mid Dorset and North Poole).
For Labour, Rupa Huq (Ealing Central and Acton), Angela Rayner (Ashton-Under-Lyne) and Melanie Onn (Great Grimsby) were among the new MPs who also signed into the Commons.
Swearing in will continue tomorrow at 11.30am.