On January 8, the American Dialect Society (ADS) voted for “they used as a gender-neutral singular pronoun for its Word of the Year for 2015.” As its official announcement continues:
They was recognized by the society for its emerging use as a pronoun to refer to a known person, often as a conscious choice by a person rejecting the traditional gender binary of he and she.
To address the problem of this binary, creations such as zie just haven’t caught on. Indeed, they is already in the language.
Singular they (and its inflected forms) has also been a point of more general contention, often decried by purists as ungrammatical. Take Every student passed their exam. Every is singular but their is plural. This disagreement drives some grammar scolds crazy, but we do it naturally all the time. Even Chaucer and Shakespeare did it. The alternative, traditionally just his, is gender-exclusive while his or her is cumbersome – and, for many, also gender-exclusive, hence the ADS’s vote.
Professor Dennis Baron and linguist Gretchen McCulloch both have excellent pieces in support of this singular they, whose history – and controversy – is much older than you may think. I really recommend you check out their pieces.
But as this is an etymology blog, I wanted to take a quick moment to marvel at the etymology of they. Caution: a little more linguistic nitty-gritty lies ahead.

They
They is English’s third-person personal pronoun, along with their and them. If I see Jack and Jill falling down the hill, I can refer to them as they. They is what many linguists refer to as a function word. Its role is grammatical. I don’t want to get too wonky here, but contrast they to a lexical item like iPhone, a coined noun, or victor, taken from Latin. (Indeed, so many of the words I study here are nouns, verbs, and adjectives borrowed from Latin, which is why they is so incredible to me, as we’ll see.) Grammatically speaking, they is just operating on a deeper level in the language, suffice it to say.
But they, amazingly, is not native to English. Starting in the late 700s and ending in the early 1000s, Vikings invaded England in three major waves. The two peoples – and their two languages – got really close. So close, in fact, that the Scandinavian form (think Old Norse) for they, þei, displaced Old English’s hīe. (For its possessive and object forms, Old English used hiera and him.) The adoption was complete by the end of the Middle English period, Albert Baugh and Thomas Cable note in their History of the English Language.
Now, Old English’s he was hē, she was hēo, and it was hit, so the Scandinavian-based they might have been a welcome source of distinction from hīe. Also, Scandinavian languages, like English, are Germanic languages, so their shared history also helps the uptake. But nevertheless, as Baugh and Cable put it: “Such parts of speech are not often transferred from one language to another.” Because such function words as they are operating so deep in the structure of the language, they are more resistant to change.
But we’re not done! English’s present plural of to be, are, may also have been influenced by Scandinavian forms. Again, Baugh and Cable:
When we remember that in the expression they are both the pronoun and the verb are Scandinavian we realize once more how intimately the language of the invaders has entered into English.
For those with non-binary gender identities, he or she can feel like an invasion, which, at least to the long, etymological view from this one writer, makes singular they all the more powerful.