Millennials frequently start companies that confront problems unique to their generation. But Inc.'s 30 Under 30 inductees for 2016 are tackling problems that have vexed society for generations, such as nefarious stock trading, hospital-borne illnesses, medication non­adherence, and reliance on nonrenewable energy sources. These young founders are taking on the planet's biggest challenges one innovative, elegantly creative solution at a time. They're setting out to change our world for the better, and not one of them doubts his or her ability to make it happen. They hail from cities large and small, have combined revenue of more than $77 million, have collectively raised more than $444 million in funding, and are shaking things up in health care, consumer products, financial services, food, transportation, energy, and more. You may not know their names now, but you will soon. Below, you'll glimpse the better future they're helping create. --Donna Fenn

Click here to see the full list of this year's 30 Under 30.

Making Hospitals Safer

Colleen Costello, 25  |  Vital Vio  |  Troy, New York
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In 2011, when Colleen Costello was a biomedical engineering student at Rensselaer Polytechnic Institute, her grandmother was admitted to the hospital for a simple fall. While there, she developed a MRSA infection and ended up being in the hospital for more than a week. "We weren't getting a lot of answers, and when I don't have answers, I like to find them," says Costello. She had been exploring ways to prevent health care-related infections, which affect one in 25 hospital patients daily. The solution: a kind of light that disinfects indoor spaces by attacking molecules specific to bacteria, mold, yeast, and fungi. She recruited her friend James Peterson, a mechanical engineering student also at RPI, for help with the light's design, and together they launched Vital Vio in 2012, their senior year. (Peterson is no longer with the company.) Unlike the UV lights commonly used in hospitals, Vital Vio's lights can be used continuously, because they cause no harm to humans. Today, Vital Vio lights are in major medical centers across the country. --D.F.

Bringing Light to Darkness

Anna Stork, 30  |  LuminAid  |  Chicago
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While many people were horrified by the  2010 Haitian earthquake, only a few acted--and Anna Stork was one of them. With a double major in engineering and studio art from Dartmouth, and in the middle of pursuing a master's in architecture at Columbia University, she was an accomplished prototyper (she built her own telescope from scratch in high school). So she teamed up with classmate Andrea Sreshta, and they scraped together recycled materials and electrical components to hand-prototype a light that doesn't need an external source of electricity. Called LuminAid, it's a floatable, solar-powered LED lantern that inflates like a balloon and collapses to become thinner than a deck of cards. To mountain climbers, it is a handy piece of cool gear. To first responders and victims of natural disasters, it's a lifesaver. Stork won't reveal how many lanterns have been sold via the company's retail channel, but since launching in 2011, LuminAid has distributed, through non­profits and NGOs, more than 60,000 lanterns for disaster relief. --Christine Lagorio-Chafkin

Snaring Tricky Traders

David Widerhorn, 28  |  Neurensic  |  Chicago
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A self-described tech nerd, David Widerhorn says he was 12 when he started his first business, which provided research on computer hardware. He'd always been fascinated by the world of finance, and as markets grew more automated, he says he became obsessed with high-frequency trading because of its technical sophistication. In 2013, Widerhorn had a eureka moment when a futures trader named Michael Coscia became the first person convicted of "spoofing," a form of market manipulation that, if done with intent to defraud, is illegal under the Dodd-Frank banking law. "It was a wake-up call for the industry," Widerhorn says. It also inspired him to turn his obsession into a business. Widerhorn and his four co-founders set to work building Neurensic, a company that uses machine intelligence to interpret individual trading activity to ensure that high-frequency traders don't break banking laws. Their core product went live in 2014. --Jeremy Quittner

Helping You Take Your Medicine

TJ Parker, 30  |  PillPack  |  Manchester, New Hampshire
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As a teenager working in his parents' pharmacy, TJ Parker saw the frustration of patients who took multiple medications. Their refills ran out at different times, and many couldn't remember which pills to take when. Parker tried to help by writing clearer instructions in Sharpie on the patients' little orange bottles, but he knew there had to be a better way. After getting a degree in pharmacy, Parker teamed with Elliot Cohen, whom he met at MIT's Hacking Medicine event series, and they launched online pharmacy PillPack in 2014. The company's customers never see a hard-to-open bottle. Instead, their pills come in easy-to-tear packets, each containing a proper single dosage, clearly labeled with the time that packet of meds should be taken. PillPack also coordinates refills on behalf of its customers (a free service) and provides online and phone support. --Kimberly Weisul

Helping Developers Create

Armon Dagar, 25, Mitchell Hashimoto, 26  |  HashiCorp  |  San Francisco
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Mitchell Hashimoto (left) taught himself programming at age 12. Armon Dadgar started college when he was 16. The two met in the University of Washington's computer science department in 2008. Dadgar was working on a project he found frustratingly tedious--porting a general scientific cloud platform onto a 2007 Windows phone. He was about to quit when the grad student overseeing the work assigned Hashimoto to work with him. Hashimoto took on the more routine aspects of the project while Dadgar brainstormed general solutions to broader problems. This contrast between the pair--Dadgar, the big-picture risk taker; Hashimoto, the detail-oriented guy looking for the perfect fix--remains their operating model at HashiCorp, founded in 2012 to build open-source tools and commercial products for software infrastructure management. The number of users for the company's open-source tools has doubled year over year since its founding. HashiCorp began charging for its products last year. --Tess Townsend

Mending Relations Between Dogs and Mail Carriers

Carly Strife, 29  |  Bark & Co.  |  New York City
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Growing up, Carly Strife was dog-deprived. "My sister and I played a lot of sports and we traveled a lot, so we never had a dog," she says. She's making up for lost time. Not only does she own three rescue dogs, but she's also co-founded Bark & Co., a dog-centric company whose products include a subscription service that mails monthly dog treats and toys to pet parents. Bark & Co. was born in 2011 when she met Matt Meeker and Henrik Werdelin, her co-founders, and they lamented the sorry state of NYC pet stores. Meanwhile, Birchbox, the subscription service for beauty-product samples, was gaining serious traction. Why not give pooches a reason to look forward to the mail carrier? Today, Bark & Co. has shipped more than 20 million products in four million subscription boxes. --D.F.

Hearing No Evil

Noah Kraft, 28  |  Doppler Labs  |  San Francisco
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As a senior at Brown University, Noah Kraft was such an impressive intern that a local film producer put him in charge of a 100-person movie crew at the age of 21. "It taught me how to run a company, make a product, and manage a team," Kraft says. A musician at heart, Kraft spent much of his youth in front of a piano or a drum set. In 2013, he co-founded San Francisco-based  Doppler Labs to turn wearable technology on its ear--literally. Doppler's sound-processing earbuds are designed to let you selectively listen to your surroundings. Want to turn up the bass at a concert or lower the sound of a crying baby? Press a button on Doppler's mobile app and you've got a volume knob for the world. "We want people to be tuned in to their environment," Kraft says, "whatever that may be." --Graham Winfrey

Turning Play to Energy

Jessica O. Matthews, 28  |  Uncharted Play  |  New York City
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At her aunt's wedding in Lagos, Nigeria, recalls Jessica O. Matthews--who grew up in Poughkeepsie, New York, and has dual citizenship--the power went out. "They brought in a diesel generator to keep the festivities going," she says. "I was 17, and it was by no means my first time in Nigeria, but for some odd reason, I was particularly bothered by the fumes coming from the generator. I started to cough and got dizzy." The experience stuck with her and ultimately led her, as a junior at Harvard, to invent Soccket, a soccer ball that captures kinetic energy and stores it in an internal generator to power the LED light that comes with each ball. "Discomfort breeds innovation," she says. Soccket, along with a jump rope called Pulse, generated more than $6 million in revenue last year for Matthews's company, Uncharted Play, founded in 2011. The products are available on the company's website, distributed worldwide through partnerships with NGOs, and private-labeled by corporate partners. Now Matthews's wildly ambitious goal is to "democratize on-demand power for everyone" by branding the micro-generator used in her products (called M.O.R.E.: motion-based, off-grid, renewable energy), which can harness the kinetic energy of just about anything that moves. Matthews plans to partner with different manufacturers to get the micro-generator into various products, like a baby stroller that could power a cell phone. "If we wanted to have the most impact and grow in a way that would allow us to do the most good, it made sense to expand beyond play," says Matthews. --D.F.