Lauren Easton, Director of Media Relations for the Associated Press, quoting the next edition of the AP Stylebook on their blog:
They, them, their — In most cases, a plural pronoun should agree in number with the antecedent: The children love the books their uncle gave them. They/them/their is acceptable in limited cases as a singular and-or gender-neutral pronoun, when alternative wording is overly awkward or clumsy.
Well it’s about time. English desperately needs a singular gender-neutral pronoun to fill the biggest functional gap in our language. Calling people “it” is offensive and crude; while “he or she” is unwieldy, and disregards the existence of people who don’t identify as either.