McDonald’s and other entities have already used food delivery services to piggyback the distribution of branded merchandise, and in a sign that this relatively new industry isn’t going anywhere soon, eMarketer reports that U.S. food delivery app usage will approach 40 million users in 2019.

This year, eMarketer forecasts that these apps will be used by 38 million people in the U.S., up 21 percent over 2018. By 2021, more than 20 percent of U.S. smartphone users will use a food delivery app. The research firm defines a food delivery app as a third-party mobile app with a primary function of ordering prepared food for delivery—Grubhub, Uber Eats, DoorDash, etc.

By 2020, food delivery app usage is expected to surpass 44 million users in the U.S., reaching nearly 60 million by 2023. In 2019, DoorDash has the highest share of consumer spending among U.S. food delivery apps at 27.6 percent, according to research firm Edison Trends. Following closely behind are Grubhub (including Seamless) and Uber Eats, which receive 26.7 percent and 25.2 percent of U.S. consumer spending in the category, respectively.

“Companies in the food delivery app space are continuing to expand and develop new partnerships with food merchants,” says eMarketer junior forecasting analyst Nazmul Islam. “As a result, customers can expect more options, which will drive user growth.”