Amid its ups and downs in the year that was, Uber is ending 2015 by celebrating a milestone: 1 billion rides.

The San Francisco-based company said in a blog post that a couple in London last night took what represents its magical 1 billionth ride. This is quite a marker for a company that has become a lightning rod in the debate over digital disruption.

“Their £5 London uberX ride together on Christmas Eve from London Fields, Hackney to Hoxton in Ara’s blue Honda Insight Hybrid was the billionth Uber trip,” the company wrote. “One billion. That’s a whole lot of riders and drivers sharing the road, special moments, and celebrations together. Certainly far more than we ever imagined when we got started in San Francisco five and a half years ago.”

That 1 billion mark underscores the tremendous momentum Uber is enjoying, despite another year of controversy and regulatory battles.

Uber has now raised at least $6.61 billion in venture capital, with reports that it is looking for even more. That investment has given Uber a valuation of more than $51 billion and a war chest that has helped it zoom past rivals like Lyft, and SideCar, which just announced it was throwing in the towel.

Still, with great valuations come great expectations. Uber continues to fight regulators across the globe, who have misgivings about the company’s impact on incumbent taxi services.

And Uber needs to make more headway in China and India, where it has run into a variety of stumbling blocks.

In China, Uber faces a well-funded rival and government opposition. Uber is still blocked on WeChat, the country’s most popular social network, which also happens to be owned by Tencent and is backing a rival service, Didi.

In India, Uber is still haunted by the arrest of one of its drivers, who was charged with raping a passenger. The result was a government ban that was instituted as rival Ola continues to raise money and expand.

More recently, Didi announced a global partnership with Lyft, GrabTaxi, and Ola in their collective fight against Uber.

Uber is hoping its ride API will expand use cases in the markets where it currently operates, as well as help it make progress in these newer markets.

But to justify its massive valuation, Uber will need to show signs of winning in India and China in the coming year. Those next billion rides will have to come a lot faster.