Sold-out arenas swelling with the thunderous applause of thousands of rabid fans. International audiences watching their favorite stars perform at the highest level. Prizes worth millions of dollars.

I’m not talking about the World Cup or the Super Bowl. I’m talking about the world of esports, where players square against one another in video games like Counter-Strike, Street Fighter, and League of Legends.

If you aren’t an avid gamer, you might be shocked by just how popular esports are. More than 40,000 fans attended the 2014 League of Legends championships in Seoul, South Korea. Some 135 million fanswatched esports events online that year. According to SuperData Research, the competitive gaming industry brought in revenue of $750 million in 2015. By 2018, that number is expected to reach $1.9 billion.

Source: Esports Are the Real Deal. Here’s What You Need to Know.