Is 2015 wearable technology’s breakthrough year? Wearables—defined as both smartwatches like Apple Watch and simple fitness trackers like those Fitbit makes—continued their massive growth in the third quarter, with 21 million units shipped worldwide. That’s nearly three times as many as were shipped in the same quarter in 2014.

A new IDC report breaks down where the 197% growth came from. A lot of it is due to Apple’s smartwatch: 3.9 million Apple Watches were shipped last quarter, good for 18.6% market share during the quarter. That’s an impressive stat considering this is only the second quarter where the Apple Watch was on sale for the entire period.

However, Apple AAPL remains the second-place vendor behind Fitbit FIT , which sold 4.7 million trackers during the same period. Fitbit remains the leader in wearables because its products are more affordable than the Apple Watch. Most Fitbits cost between $50 and $200. The least expensive Apple Watch starts at $349.

Fitbit’s success is another sign that smartwatches aren’t replacing fitness trackers, as has been theorized. Instead, analysts said that smartwatches and fitness trackers are co-existing. Both product categories are growing year over year, and the market is diversifying into a range of products with different features from simple step tracking to a smartphone-like experience on your wrist.

Xiaomi doesn’t make a smartwatch yet, but it shipped more wearables than any company other than Apple and Fitbit last quarter, due to its Mi Band, which is primarily sold in China. The low-cost fitness tracker costs just $15, and Xiaomi added a heart rate sensor to its latest model, which went on sale during the past quarter.

After the top three vendors, there’s a huge drop in total units shipped. Garmin GRMN , which makes GPS-equipped fitness watches, sold 900,000 devices in the third quarter of 2015, good for fourth place. And in an upset that shows just now nascent the market is, the fifth biggest wearable vendor last quarter is a Chinese company nearly completely unknown in the United States. XTC, a subsidiary of BBK, shipped more wearables than Korean electronics giant Samsung last quarter. It shipped 700,000 units of its one device, the Y01, a phone-watch hybrid intended for children sold exclusively in China.

Other notable companies missing from IDC’s leaderboard include Jawbone, which makes the Up fitness tracker, and recently had to to lay off 15% of its employees. None of the five top wearable vendors make a smartwatch running Google GOOG Android Wear software, either, indicating that Apple’s WatchOS is the dominant smartwatch interface for now.

The absence of Android Wear is mostly due to the fact that the latest devices, such as Fossil’s new watch, didn’t go on sale until late in the quarter, IDC research manager Ramon Llamas explained in an email to Fortune. “The (Android Wear) vendor list is rather short. Samsung bowed out, and it’s mostly Motorola and a few Chinese vendors just getting going.”

But the entire wearable industry is growing rapidly right now, and there’s room for new companies and software platforms to come in and establish a foothold as more people try wearable technology for the first time. The next question facing the industry is the 2015 holiday season: How many people will find wearables under the tree this year?

For more on the wearables market, watch this Fortune video:

Subscribe to Data Sheet, Fortune’s daily newsletter on the business of technology.