The choices when we make when we get dressed express more than just our style. They connect us to a global industry that has massive impact on people’s lives.

When the sneaker industry got going around the middle of the 19th century, the shoes were a niche product—footwear for the rich sport of lawn tennis (hence the enduring term “tennis shoes”).

By now they’ve so far transcended just athletic use that market-research firm NPD Group forecasts “sport leisure” sneakers—the casual sort, as opposed to performance shoes meant specifically for athletic use—will become the largest footwear category in the US in 2020. The incumbent front runner they’ll overtake is what NPD calls “fashion” footwear, a category including most of everything else: shoes, boots, sandals, and slippers.

It will mark a major milestone for sneakers, not least of all because the US is one of the world’s two biggest fashion markets. Sneakers have become integral to the way people dress (Quartz member exclusive). They’re so ubiquitous that it may surprise some to learn casual sneakers weren’t already the top category recorded by NPD. But the shoes had a lot of ground to make up. Sneaker makers also haven’t historically paid as much attention as they could have to women, a large and valuable customer group, and as indicated, their numbers also don’t include performance sneakers, for good reason.

Many of the shoes may have begun as athletic footwear, but sports are no longer their main purpose, as in the case of shoes like the Nike Air Force 1, retro Jordans, or Converse All Stars. Others were never intended for sports to begin with, such as Allbirds or Yeezys. NPD’s prediction is that styles with their original roots in running and basketball will lead sport leisure’s growth, most of it coming from the men’s and kids’ markets.

The impending dominance of these lifestyle sneakers is due to the ascent of athleisure, which you could describe as the recent pronounced uptick in a century-long process that’s brought sports clothing into our everyday wardrobes as clothes get more casual and comfort becomes an ever-greater priority. Americans are embracing healthy lifestyles, but are also less committed to specific sports, explained Matt Powell, NPD’s senior industry adviser for sports. They want shoes that are versatile, comfortable, and functional across their everyday lives, allowing them to go to work or the gym without having to change. As a consequence they’re less interested in sport-specific technical performance, which is why last year casual sneakers became the top-selling sneaker category in the US.

This shift is happening at the expense of performance and fashion footwear. According to NPD’s data, which tracks sales across most of US retail—though not direct-to-consumer sales by brands—sport leisure grew through the 12 months ended in August. Sales of both fashion and performance footwear declined. (If you do take into account direct sales by sneaker brands, casual sneakers could overtake fashion footwear even sooner as those sales are quickly on the rise.) It even forecasts that the shift to more sport-inspired shoes is going to have a chilling effect on sales of “the thong, flip-flop, and ballerina segments.”

Sport-inspired casual shoes seem likely to widen their lead over non-sport styles through 2021. Next year, NPD predicts sport leisure sales will exceed those of fashion footwear by about 3%. The following year, it will widen to about 8%.