It’s hard to believe Juul Labs, the leading e-cigarette maker in the U.S., is only three years old.

Considering the $15 billion startup has grown to control nearly 73% of the e-cigarette market, it’s easy to see why the U.S. Food and Drug Administration has focused the scope of its regulation efforts largely on the San Francisco-based unicorn.

Just this week, the FDA announced it conducted an “unannounced on-site inspection” at Juul Labs headquarters in San Francisco after the agency’s commissioner Dr. Scott Gottlieb decried the growing prevalence of e-cigarette use among high schoolers as reaching “epidemic proportions.”

Earlier in September, the FDA ramped up efforts to curtail underage use of e-cigarettes by requiring Juul, as well as British American Tobacco’s Vuse, Altria’s MarkTen, Imperial Brands’ Blu E-cigarettes and Japan Tobacco’s Logic, to share a plan on how they will prevent teenagers from using their products. The FDA gave them 60 days to comply.

Juul said it “will submit a comprehensive proposal to address underage usage within the 60-day timeline,” declining to elaborate.

As we await the proposal, here’s what we know about Juul.

Juul becomes a behemoth

Juul’s rise dates back to 2004, when Stanford University graduate students James Monsees and Adam Bowen were taking a smoke break from brainstorming topics for their joint master’s design thesis. Their shared desire to quit smoking led them to seek a new way to deliver nicotine, which the duo used to found Pax Labs (formerly called Ploom) in 2007.

Nearly 10 years later, the company introduced a new product that quickly upended the e-cigarette market: The Juul. Shaped like a sleek USB drive with a minimalist design, it quickly earned its title as “the iPhone of vaping” by many reviewers. The patented technology behind it boasts the quick hit of nicotine expected from a traditional cigarette, with the ease of use that came with replacing its Juulpod cartridges that pack as much nicotine as a pack of cigarettes. The Juul starter kit, which includes the rechargeable e-cigarette and four Juulpods, retails at a slight premium to its competitors at $49.99.

Impressively, Monsees revealed in an interview with CNBC the 20-person team that launched Juul in June 2015 was able to do so on a budget of $2 million. Its success within just two years led to Pax Labs spinning Juul Labs off in 2017.

Sales in the 52-week period, ending in November 2017, topped $224 million, representing 32% of the entire e-cigarette category, according to Nielsen sales data cited by Wells Fargo analyst Bonnie Herzog. By April, Juul’s market share doubled to top 60%. As of September, Herzog’s same report showed Juul’s 52-week sales grew 770% over the same period a year ago to top $1.47 billion, representing nearly 73% of the entire category. Juul said the bulk of its sales, roughly 90%, come through retail brick-and-mortar locations.