On Thursday, the world's best professional golfers will tee off in Oakmont, Pennsylvania, for the 116th U.S. Open. Thousands of spectators will be on hand for the tournament, with millions more watching on television, many wishing their own game were anywhere near as good. While smaller in number than fans of other sports such as football, golf's pool of enthusiastic duffers still adds about $70 billion to the  U.S. economy each year, according to industry experts. And yet, some say, golf's got a major problem: It doesn't appeal to millennials.

Before you sigh, understand that the many young people do play. According to a two-year  study conducted by the National Golf Foundation, a research group, millennial golfers (defined by the NGF as 18- to 34-year-olds) currently number around six million in the U.S., and account for $5 billion of annual golf-related spending. But the younger crowd is dwindling. The study found that 400,000 more people left golf in 2013 compared with the previous year; of that number, half were millennials. And since traditionally players first get into the sport when they're in that age range, it's pretty crucial for the community to beef up its numbers.

According to the NGF study, there are about 12 million millennials who are considered "latent demand"--they're non-golfers who might be enticed to putt around a bit. And then there are the golfers who dabble--nearly 30 percent of the total millennial golfing population--who might be persuaded to play more.

Several innovative companies are attempting to revive interest within the millennial demographic, and in doing so are making golf more user-friendly, more social, and more accessible. Here's a look inside five businesses guiding the sport into the future.

1. Topgolf

You might call this two-time Inc. 5000 honoree the millennial whisperer of the golf world. Dallas-based Topgolf, which opened its doors in 2000, turns the typical driving range model on its head. Using microchip-embedded golf balls and landing areas made up as targets, the "golf entertainment complexes" open the sport up to the masses. Originally marketed to serious golfers and families, Topgolf really hit its stride by pivoting toward the younger crowd. The addition of DJs, high-end fusion food, a cocktail menu, and even themed parties has allowed the chain to create serious buzz about the sport by attracting a crowd that wouldn't necessarily sign up for a 9- or 18-hole round. Whether or not it's encouraging people to pick up a set of clubs for a real game is harder to tell, but the business model is working. Topgolf now has 26 locations around the world, including a new Las Vegas location.

2. Big Hole Golf

Don't expect the fusty old-school golf crowd to like this one much. Perhaps the wackiest--yet most straightforward--idea on the list, Australian company Big Hole Golf attempts to cut down two barriers to entry at once: For many beginning golfers (not just millennials), the sport is just too dang hard. Also, it is, by nature, an exceedingly slow game. By expanding the size of holes on traditional golf courses (by about twice the regulation diameter), Big Hole Golf has created a new playing style called fastball, which the company says can entice social golfers onto the links. Close to 30 golf courses around the U.S. now host Big Hole events, allowing the establishments to cash in on casual players who want to spend some time on the green without paying for a pricey country club membership.

3. GolfTEC

Founded in Denver in 1995, GolfTEC offers a modern spin on traditional golf instruction. Private golf teachers lead one-on-one lessons, giving feedback based on data from body sensors, launch monitors, and video cameras. Rather than relying solely on a coach's powers of observation, students' body movements are compared directly with data from the swings of 150 PGA Tour pros to give quantitative, precise data. By shortening the learning curve and bringing lessons into urban centers--they take place primarily in storefront 'pods' rather than on a course or driving range--GolfTEC allows players to learn the game even if they can't travel out to the 'burbs.

4. Looper

File this one in the category of, "It's like Uber, but for (fill in the blank)!" Virginia-based Looper Golf makes an eponymous app that connects caddies with players, giving older golfers on-demand access to people to carry their bag, while facilitating one of the most common entryways for young people into the sport. Caddies register with the program and study Looper's caddie education materials. They then take an online certification test, and attend an orientation in their local area. After that, they're ready to be hired at one of Looper's participating clubs and courses, turning golf into a profitable pastime and, hopefully, getting them into the habit of spending time on the course. The app, which launched this spring, already has 14 courses across Virginia and Maryland, and will expand to cover five more states by next spring.

5. Arccos Golf

Traditionally, golfers have only had one metric to gauge skill level: their handicap. Connecticut-based Arccos Golf wants to change that, and in doing so, make golf more accessible. Using 14 lightweight screw-in sensors--one for each club in a player's bag--and a smartphone app that syncs with the sensors to record data like driving accuracy and distance, players can learn from their mistakes in a more holistic, data-driven way, making even novice players feel more like the pros. By interfacing with detailed GPS maps of the course they're playing (Arccos has almost 40,000 courses mapped already, and can generate new ones at request, usually within 24 hours), golf suddenly becomes a little less guesswork, and a little more modern. Plus, Arccos sells their products in über millennial-friendly Apple  retail stores.