Upwork, the world’s largest freelancing website, today released its latest quarterly index of the hottest skills in the U.S. freelance job market. The Upwork Skills Index ranks the marketplace’s 20 fastest-growing skills being hired for among freelancers — now 35 percent of the U.S. workforce.

The 20 fastest-growing freelance skills in Q4 2016 all experienced more than 100 percent year-over-year growth with the top 10 experiencing more than 200 percent year-over-year growth.