UK passports currently have "M" or a "F" for people to specify their gender - but what about "X"?
A campaigner has today been given the go-ahead to challenge the government over gender-neutral passports.
Christie Elan-Cane wants there to be an "X" - which stands for unspecified - for people who don't identify as male or female.
Transgender blogger Mia Violet, who backs the call, says it would be a sign of "respect" to trans people.
She says it's fantastic the campaign has taken its next step and describes it as a "sign of progress".
"Trans rights do feel as though they've stagnated in the UK and I do hope this pushes forward more changes.
"We need to ensure everybody is recognised. For trans people to be seen, I think that's going to be incredibly important to them because so often they are overlooked."
Mia, 28, from Dorset, came out as transgender around two years ago.
She told Newsbeat: "Initially, I identified as non-binary. I didn't see myself as fully female or fully male, I was kind of in the middle.
"Over time, I've become more comfortable with using female to describe myself. But it was very awkward and uncomfortable in that time because there was basically no way to select a gender that felt like mine."
Mia says gender-neutral passports in the UK would be an important step because "it's recognition and it's respect".
"When I changed my passport gender to female, I had to get a letter from my doctor that basically said 'OK Mia is trans. This transition is permanent. She is now considered female, please change it'. It wasn't enough for just my permission to do it.
"It's almost like the government is looking the other way and not really thinking about trans issues but at the same time we have thousands of thousands of trans people in this country who are having to deal with systems that are just not set up to recognise them."
Christie launched a High Court fight for the right to have "X" passports in the UK. The campaigner has now been given permission to challenge the government in a judicial review.
Christie believes it's wrong to force people to choose either M or F on their passports if they define as neither.
Gender-neutral passports are already available in Australia, New Zealand, Denmark, Germany, Malta, India, Nepal, Pakistan, Ireland and Canada.