Why Harry Didn't Die

From the books:

''"Precisely!" said Dumbledore. " He took your blood and rebuilt his living body with it! Your blood in his veins, Harry, Lily's protection inside of both of you! He tethered you to life while he lives!"''

-Page 709, Harry Potter and the Deathly Hallows

"He took your blood believing it would strengthen him. He took into his body a tiny part of the enchantment your mother laid upon you when she died for you. His body keeps her sacrifice alive, and while that enchantment survives, so do you and so does Voldemort's one last hope for himself."

-Albus Dumbledore, Page 710, Harry Potter and the Deathly Hallows