The joke among young men these days is that everybody’s got a little money riding on something: football games, foreign elections, the odds of a U.S. military strike. Except it’s not really a joke. I recently made $3.79 guessing when the United States would attack Tehran. I pocketed $0.85 when To Lam was re-elected general secretary of the Communist Party of Vietnam. I took home $83.64 after the rock climber Alex Honnold successfully climbed the skyscraper Taipei 101 without a rope.

My wagers were all placed on a prediction market site called Polymarket. Polymarket is sort of like the Nasdaq or the New York Stock Exchange, except instead of buying and selling shares of publicly traded companies like Apple or Microsoft, the platform allows you to trade on what will happen in the future. Who will win the midterms? How much will the Fed cut rates next month? Will the government shut down? Well, it did — and I lost an entire month’s rent. That one really hurt.

Polymarket and its main rival, Kalshi, are the two largest prediction markets in the world. My wagers were a drop in the bucket; together, the two platforms processed $25 billion in trading volume in April — up tenfold from a year ago. (That’s roughly one-fiftieth of 1 percent of the volume traded on the Nasdaq.) Both platforms insist that they’re not gambling websites — and that their users trade on “event contracts” rather than place bets — but, in any case, they’re becoming mainstream. Polymarket has inked exclusive partnerships with the parent companies of The Wall Street Journal and the New York Stock Exchange; Kalshi has announced agreements with CNN, CNBC, The Associated Press and Fox News. Nearly 40 percent of American men between the ages of 18 and 34 have made a trade.

Getting here wasn’t straightforward. Not long ago, the government was trying to shut the platforms down. In 2022, during the Biden administration, the Commodity Futures Trading Commission — which, in addition to regulating prediction markets, oversees derivatives exchanges for more traditional commodities such as wheat and lean hog and oil futures — effectively banned Polymarket, which is cryptocurrency-based, from serving American customers. The company shut down its U.S.-based operations and relocated to Panama. A year and a half later, the commission blocked Kalshi from permitting users to speculate on which political party would control Congress. Kalshi went to court. In the fall of 2024, Kalshi won its case against the C.F.T.C., opening the door to legal election betting in the United States.

Prediction market traders wagered billions of dollars on Kalshi and Polymarket during the 2024 presidential race. Days after the election, the F.B.I. raided the home of Polymarket’s chief executive during an apparent investigation into whether the company had allowed U.S. users to trade on the site. (The C.F.T.C. and the Department of Justice later closed the investigations without bringing charges; the C.F.T.C. has also become friendly to the industries it regulates, which have deep ties to the Trump family.) In July 2025, Polymarket purchased a federally licensed derivatives exchange and clearinghouse, which helped them secure C.F.T.C. approval; as of this writing, users in the United States can bet on a couple of political markets, 10 weather markets (for instance, the high temperature tomorrow in Miami) and a lot of sports.

On Kalshi, sports wagers are the largest betting category, accounting for roughly 70 percent of all revenue on the platform. But users on both platforms can wager on just about anything: the price of Bitcoin; the duration of Donald Trump and Xi Jinping’s handshake; whether the headlines on the front page of this newspaper will use the word “stupid” in a given week. Unlike a sports-betting app or a casino, there’s no house, just other bettors on the other side of each trade: Every dollar you lose is a dollar won by someone else.