Thanks to a variety of factors, including lower startup costs and technological advances, many of the world’s most taxing problems are being tackled by some of the youngest entrepreneurs. To put this in perspective, we turned to the Kairos Society, an international organization that supports the development of entrepreneurs worldwide. Each year, the San Francisco-based company develops a list of the top global entrepreneurs under age 25. Now in its fourth year, the list is culled from 550 nominations, many of which come from members of Kairos' regional chapters.

Present listees get the chance to demo their companies at this year’s Kairos Global Summit in Hollywood, California in October. And one lucky winner could land $50,000 from Ev Williams, the Twitter co-founder. By way of his venture capital firm, Obvious Ventures, one winning company, which successfully demonstrates an innovative solution to a global problem, will get an uncapped note for $50,000 as an investment. Listees also join the ranks of illustrious past winners, such as Boston health-care tech company WellFrame and the Menlo Park, California-based drone maker Lily Robotics, which both went on to raise significant capital and media buzz.

The hundreds of nominations received this year were whittled down to 50 finalists by Kairos team members and industry professionals, who evaluated each founder's company on the feasibility of its vision and pointed out any potential technical traps the company might face. A new criterion this year was that each company on the list was required to have either a finished product or prototype, says Kairos Society CEO Alex Fiance. The judges also look for founders with companies in industries with great potential for disruption, such as education and healthcare. Finally, and perhaps most importantly, they're looking for founders with "a bit of delusional optimism,” says Fiance. “[They must] believe they can enter and change billion-dollar industries,” he adds.

Here’s last year’s list of the top 50 emerging global entrepreneurs to watch.