For Parker, a self-taught polymath, deep questions often lead to ambitious action. Long fascinated by the human immune system, he spent $250 million to create the Parker Institute for Cancer Immunotherapy. Curious about his life-threatening peanut allergy, he funded the Sean N. Parker Center for Allergy & Asthma Research at Stanford. His interest in the music industry led to the Sean Parker Institute for the Voice at Weill Cornell Hospital in New York. So it’s not surprising that he’d eventually turn to policy. From the beginning, Parker’s Economic Innovation Group, backed with $15 million, focused on the causes of inequity and the potential of using tax policy to force profits out of portfolios and into poor neighborhoods. “Peter Thiel bet me a million dollars that I wouldn’t get it done,” Parker says. “So that was part of my motivation.”

He’s a hard guy to bet against. In 1999, along with Shawn Fanning, he cofounded the free online music-sharing platform Napster, which blew up the recording industry—and later itself after triggering an avalanche of copyright lawsuits. In 2004, after seeing Facebook on a friend’s computer, he used his Napster fame to score a meeting with a young Mark Zuckerberg at a Chinese restaurant in New York. He spent the next year as Facebook’s first president, scaling the startup before clashing with investors, exiting with enough equity to give him a current net worth that Forbes estimates at $2.6 billion. He then became an early backer of Spotify, playing a large role in bringing the then-nascent Swedish streaming startup to the U.S.

More recently, Parker has turned his intense focus to philanthropy, donating more than $400 million in the past four years—a decent chunk, given that he’s still in his 30s. For the problem of blighted neighborhoods, however, Parker sees his tax-avoidance policy as a better play: “You’ll never solve domestic poverty by giving your money to a foundation. That’s not going to achieve anything. What you need is trillions of dollars in investor capital.” Parker built the Economic Innovation Group to be independent, bipartisan and pragmatic, “basically representing the poor people in America.” To run it, he recruited Steve Glickman (a former senior economic advisor to President Obama) and John Lettieri (a government-affairs veteran who served as a foreign-policy aide to Senator Chuck Hagel). His economic advisory board included Kevin Hassett, Trump’s chief economist, and Jared Bernstein, who held the same job for Vice President Biden.

The think tank quickly focused on crafting a policy that uses tax incentives to move investor cash into struggling communities. The group met with hundreds of lawmakers to share findings, hear feedback and build a base of supporters. Parker would visit Washington every few months for a marathon of meetings, slowly garnering promises of support. Parker boasts that he walked the congressional corridors until his feet ached and would lob late-night calls to top lawmakers for updates on the initiative. As the idea crystallized, other wealthy entrepreneurs, including Steve Case, Jim Sorenson and Michael Milken, jumped on the bandwagon.

By 2016 the Opportunity Zone bill had won the support of 72 legislators from both parties. It was ideological surf and turf. For Republicans, it promised a tax cut, a market-based solution and a way to put power in the hands of state and local governments. Democrats, meanwhile, liked the prospect of pouring money into areas in dire need of funding. Also in the idea’s favor: It was new. “If you come up with something that’s completely novel,” Parker says, “there’s no organized opposition against it.”

That April, toward the tail end of the Obama administration, Scott and Booker introduced the bill on the Senate floor while Congressmen Pat Tiberi (R-Ohio) and Ron Kind (D-Wis.) proposed it in the House. They toyed with attempting to pass it as a stand-alone law but decided it was best to wait for some fast-moving legislation to hitch it to.

Parker had held a fundraiser for Hillary Clinton at his L.A. mansion, but Donald Trump’s surprise victory—and the GOP’s subsequent push to cut taxes—offered him an unexpected ride. “The opportunity was one that I thought was horrible—but Tim Scott thought was awesome,” Booker says. “But for our bill, this was perfect, and we decided to make it part of the larger tax reform.”

By now they had a bipartisan group of roughly 100 lawmakers sponsoring the bill. Speaker Paul Ryan and Senate Finance Chairman Orrin Hatch backed it.

Despite that broad support, O-zones were left out of the version of the tax cut passed in the House. A savior was Tim Scott, who had met with Trump and says he got the president’s blessing for the provision. The bill’s early sponsor, Scott was also a member of the Senate Finance Committee. He maneuvered to get O-zones into the Senate version of the bill. Once in there, the O-zone clause had life—but could very easily have been removed by the conference committee, a small group that worked out differences in the House and Senate versions of the bill.

The years that Parker and EIG had spent building a base paid off. “You prove that you’re really into it—and that you’re not going away,” he says. Many conference-committee members had been O-zone sponsors. When President Trump signed the tax bill into law in December, the initiative was in there, but it was little-understood or hardly noticed.

The law’s engine is a new breed of financial product, the opportunity fund, that offers investors a trifecta of attractive tax breaks. Here’s how it works. Investors who sell assets have 180 days to plow their taxable capital gains into an approved opportunity fund, which must hold 90% of its assets in Opportunity Zone projects. To put money to work fast, the law requires that the funds invest all of their cash within some specified time frame. (The Treasury Department is still deciding on that and other crucial details.) Tax on the original reinvested gain isn’t due until 2026, and the taxable gain is cut by 15%. Meanwhile the new opportunity investment grows tax-free, like a Roth IRA, provided it’s held for at least ten years. (If it’s sold earlier, it can be rolled into another opportunity fund and remain tax-free.)

For a census tract to qualify as an O-zone, it must have a poverty rate of 20% or higher or a median household income that is less than 80% of the surrounding area. Governors are allowed to designate 25% of their states’ eligible tracts as O-zones. In all, about 8,700 areas, ranging from rusty industrial towns to dusty rural hamlets, have been approved.

Unlike previous development incentives such as Enterprise Zones and New Market Tax credits, which capped tax benefits and placed restrictions on the industries and regions you could invest in, the O-zone law is broad and scalable. Vice businesses (liquor stores, casinos, massage parlors) are barred. And while venture capitalists, private-equity shops and banks will be essential for launching opportunity funds, those firms can’t simply locate in an O-zone and grow tax-free. Other than that, the investment options and those who can invest are broad.

“The great thing about this legislation is it can bring together sectors that may not have worked together before,” says Jim Sorenson, a Utah-based entrepreneur and impact investor who was an early part of Parker’s coalition. “There can be a great collaboration between state and local entities to add more incentives to further sweeten the pot.”

Sorenson says philanthropy can play an important role in prepping an O-zone for growth, providing initial capital to secure real estate loans or launching job-training programs to create a large supply of local talent ready to work. “We can come in first, solve problems and de-risk projects to make them more feasible for investors,” Sorenson says. “Then you tap into the institutional markets—that’s where the big money is.”

Big money can come from a host of sources: real estate developers, PE funds, venture capital, investment banks, wealthy individuals, family offices and mutual funds. And there are many places for big money to go. Rural communities can host projects that need wide spaces, like farming, energy, mining, data centers and labs. Cities are likely to attract real estate developers, startups and venture funds.

For real estate developers, O-zones offer cheap real estate and unlimited, untaxed upside if a neighborhood takes off. Developers must do more than stash cash in crumbling property. To qualify for tax perks, they must make swift and significant upgrades (at least equal to the cost of the initial purchase). With real estate projects come new office buildings, industrial districts, restaurants and affordable housing—all of which can lay the groundwork for an economic boom. “The real estate aspect is a great catalyst to attract new businesses,” says AOL founder Steve Case, an early supporter of the O-zone initiative, whose Rise of the Rest Fund invests in backwater areas. “But it’s the startups that will be the real job creators.”

For venture firms, which tend to make many small, risky bets with the hope that a few will be blockbusters, backing O-zone startups can carry unbelievable gains. Under the law, VCs can plow returns into opportunity funds, deferring taxes and setting the stage for a future tax-free windfall. “If Facebook could have chosen to locate itself in an Opportunity Zone, like the Tenderloin in San Francisco, the investors would’ve paid no capital gains on their equity,” says Parker, who presumably would have been one of the big winners. The promise of mega-returns could send VCs, investment banks and private equity firms scrambling to launch their own opportunity funds to create incubators, scour second cities for overlooked talent or move portfolio companies into O-zones. “It wouldn’t surprise me if a lot of Silicon Valley VCs started to tell founders, ‘We’d like you to go over the bridge to Oakland, or we’d like you to go to Stockton,'” Parker says.

If they do, they’ll find a welcome wagon. “We started at zero. We were the foreclosure capital, our homicide per capita highest in the nation, we declared bankruptcy,” says Stockton mayor Michael Tubbs, a charismatic 28-year-old Stanford grad who returned to his hometown following a cousin’s murder. “We’re not afraid of the future. We’re not afraid of new. We’re not scared of Opportunity Zones. Let’s do it.”

Stockton is a good example of what could be: 90 minutes from San Francisco and 45 minutes from Sacramento, it’s surrounded by agrarian possibilities yet crippled by high costs, high unemployment and high crime (in 2011, Forbes named it America’s “most miserable city”). Roughly 25% of its 300,000 residents live in poverty.

Tubbs envisions new apartments in its bleak downtown, industrial parks along its airport corridor and a waterfront “like the San Antonio Riverwalk, where people can live and work,” complete with hipsters and beer gardens. To make it happen, he’s already preparing formal pitches for opportunity funds, forging strategic committees with the local government and business, real estate and academic leaders to surface potential and streamline action. Past that, “I’m not going to share all my secret sauce with other cities,” he says.

The joke betrays a fierce competition brewing. It’s likely that only a handful of the roughly 8,700 designated O-zones will attract the critical mass necessary for a significant turnaround—or investor confidence. “There will be a herding mentality and a domino effect,” Parker says. “The more momentum an area gains, the more investors it will attract.”

“It’s like the Amazon headquarters battle,” says Margaret Anadu, the head of Goldman Sachs’ Urban Investment Group. “It has mayors and regional players asking, ‘What great things does my city have to offer? What are the challenges? What are my plans to address them?’ “

Where Opportunity Zones go, opportunists will follow. The law’s rich tax perks will lure many players more interested in the program’s tax benefits than its societal ones. The broad and flexible nature that gives the plan its power also leaves ample room for abuse, loopholes and unintended consequences. With billions in for-profit capital likely to flow into poor communities, there’s a chance that the very people the program is intended to lift up could instead get pushed out. Nearly everyone Forbes interviewed for the story agreed that gentrification is a real risk.

The answer for Mayor Michael Tubbs is local control, with the government steering investments to places where capital would make a sizable impact. “We don’t have many people living in our downtown, so new housing wouldn’t be displacing people but bringing new people in,” Tubbs says. “You’d be making downtown safer and bringing in units that people can afford.”

For Booker, it started with governors choosing Opportunity Zones that show no sign of current gentrification. He says leaders must ensure that a large portion of locals are hired to build and ?service new projects and that towns adopt and enforce zoning and affordable-housing laws as new capital flows into the community.

“The whole point of this is creating opportunity for the people who are living in those places today,” Goldman’s Anadu says. “If the investments don’t provide better housing, better jobs, an increased tax base and better government services, then it’s been a big waste of time and we’ve all failed.”

On the flip side, what happens if the program is too successful? What if the next Facebook moves just a few miles into a neighborhood O-zone like East Palo Alto, vaporizing tens of billions in capital gains without really transforming a city? Or if it just accelerates a Brooklyn-like real estate boom that would have happened soon anyway? “You can paint all types of possible scenarios,” says Senator Scott, “but I have 50 years’ worth of evidence showing the risk of doing nothing.”

For now, it’s a waiting game. Treasury and the IRS are scheduled to hand down the final O-zone rules by the end of 2018. Investments could conceivably start early next year. Until then, investors wait on the sidelines as mayors perfect their pitches.

Parker, meanwhile, is steering his think tank to create new policies. “I came away with an optimistic view about members of Congress,” Parker says, voicing a sentiment precious few have echoed in the past 20 years. “They want to talk about an idea that can move the needle and fix the structural issues facing the country. There’s probably a bunch more of these things out there that we can do.”