Shadow home secretary Yvette Cooper has become the fourth Labour big-hitter to announce she is standing for her party's leadership.
She joins the race alongside Chuka Umunna, Liz Kendall and Andy Burnham, who also announced his candidacy today.
After last week's huge general election defeat, Ms Cooper said the Labour Party had not given voters enough hope.
She 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".
In an article for the Daily Mirror, Ms Cooper pledged to make life better for families as she threw her hat into the ring to replace Ed Miliband, with the new leader to be announced at a special conference on September 12.
She wrote: "In the end, Labour didn't convince enough people that we had the answers. They liked a lot of what we had to say, about raising the minimum wage, expanding childcare, cutting tax for low-paid workers and banning bad zero-hours contracts. But for many people it wasn't enough to give them hope and confidence we could match all their ambitions for the future.
"And when there's too little hope, optimism or confidence, the politics of anger, fear and division takes over - that's what the Tories, the SNP and Ukip all exploited and campaigned on in this election.
Ms Cooper sought to distance herself from New Labour, a movement some within her party have called for a return to.
"Going back to the remedies of the past, of Gordon Brown or Tony Blair, won't keep up with the way the world has changed," she said.
"We need a Labour Party that moves beyond the old labels of left and right, and focuses four-square on the future. Credible, compassionate, creative, and connected to the day-to-day realities of life."
