The next Labour leader will be announced on September 12, with big names from different generations of the party in the running to replace Ed Miliband.
Declared and potential candidates include:
• Andy Burnham
Having finished fourth out of five in the last leadership contest, the shadow health secretary is likely to be the unions’ favourite this time.
He has strongly opposed further privatisation in the NHS - in contrast to his deputy, Liz Kendall, who is also in the leadership race.
A passionate Everton fan, he won kudos for his role in the last Labour government in securing the reopening of the inquiry into the Hillsborough disaster.
But he is potentially vulnerable over his role of health secretary at the time of the Mid Staffs hospital scandal.
Launching his leadership bid, Mr Burnham signalled that he wanted to return the party to the treble election-winning approach adopted under Tony Blair.
He said he wanted Labour to “speak for everyone and for the whole country” and address voters’ aspirations the way it did in 1997.
• Yvette Cooper
The current shadow home secretary served as housing minister, treasury chief secretary and work and pensions secretary in the last Labour government.
Long tipped to be the party’s first woman leader, one potential obstacle to a tilt at the top job - the leadership ambitions of husband Ed Balls - was removed when he was ousted by the voters of Morley and Outwood on election night.
Her links with the Blair-Brown years may nevertheless count against her if the party feels that it needs to make a decisive break with the past.
Launching her campaign, she rejected calls to “go back to the remedies of the past” that worked for Mr Blair.
Ms Cooper said she wanted Labour to “move beyond the old labels of left and right” and be “credible, compassionate, creative and connected to the day-to-day realities of life”.
• Liz Kendall
The ambitious shadow health minister was the first to declare her hand in the leadership contest, despite having yet to reach the shadow cabinet.
Part of the 2010 intake of MPs, she will look to appeal to Blairites with her pro-market declaration that “what works” should be the priority for the NHS and her call for the party to reach out to the aspirational middle-classes.
A former special adviser to Harriet Harman and then Patricia Hewitt - whose Commons seat in Leicester she inherited - she may be seen by some as too much of a Westminster insider. Supporters point to her working-class Watford background in her favour.
• Chuka Umunna
Another new arrival in 2010, the shadow business secretary was initially seen as leaning towards the left of the party - he backed Ed Miliband for the leadership and served as his parliamentary private secretary.
Since taking on the business portfolio, he has talked more about the importance of enterprise and aspiration and discusses strategy with the godfather of the Blairites, Lord Mandelson.
A lawyer by profession, he is seen as a smooth and accomplished media performer - but used an amateur video shot on the streets of Swindon to declare his intention to stand.
He said he believed Labour could win power in five years’ time, adding: “I want to lead that effort as part of a really big Labour team, getting Labour back into office.”
• Tristram Hunt
A third member of the 2010 intake, the shadow education secretary is widely tipped to enter the race.
Seen by some as too posh, others believe the privately-educated TV historian has the charisma and appeal to win back the Middle England voters who conspicuously ignored the party at the election.
He has said Labour must “realise the scale of the defeat, the full-blooded rejection of our policies, and the necessity for a total reappraisal”.
He believes that “we can only achieve a Labour government if we can combine a compassionate story about supporting those who need it most with a sense of optimism and hope for those who aspire to climb life’s ladder” , an offer of “empathy and entrepreneurialism” that helped sweep the party to power under Mr Blair in 1997.