Facebook users who don't identify as either "male" or "female" will finally be able to customize their gender identity — and preferred pronouns — on their profiles. The changes went live for the site's 159 million users in the U.S. on Thursday. Facebook disclosed the changes to the Associated Press just before rolling them out. 

Facebook software engineer Brielle Harrison explained the importance of this change to the AP: "There's going to be a lot of people for whom this is going to mean nothing, but for the few it does impact, it means the world." Harrison identifies as TransWoman, an option she can now also display on her page. She added: 

All too often transgender people like myself and other gender nonconforming people are given this binary option, do you want to be male or female? What is your gender? And it's kind of disheartening because none of those let us tell others who we really are.

Until recently, Facebook only offered a few gender options for users: you could identify as male, as female, or as a hidden, "neutral" option. Now, individuals can choose from about 50 different identities by going to their profile, opening up the "edit" box for their basic information, and changing the drop-down gender option to "custom:" 

That brings up a new menu for the site: 

Where users can set their preferred pronoun (the choices are him, her, and them), specify their gender identity as one of 50 pre-loaded options, and change the privacy settings on who gets to see it. 

As you can see from a quick survey, there are a lot of different options, the result of a series of consultations with trans activists. Facebook plans on rolling out the change worldwide in the coming months. 

So how does this impact advertising? That's a little trickier. Facebook does target ads at users based on their gender selection. According to the AP, the site will now use the preferred pronoun as its basis for targeting ads at users with "custom" gender identities. Facebook also won't mark a gender change on its site as a life event (like, for instance, getting engaged), meaning that those who have recently changed how they identify on Facebook won't end up with ads targeting them as recently trans. 

Facebook announced the change with a post on its own site: 

 

And have updated their help page for editing user info accordingly.