Eager to leap in where so many others have stumbled, Silicon Valley investors have been pumping capital—$1.2 billion in 2015 alone—into startups taking on the task of improving health insurance for individuals and employers. It’s not for the faint-hearted: The industry is rapidly consolidating, making it harder for new companies to gain traction. But the payoff could be huge. “It’s a big, juicy opportunity with a lot of market cap,” says Sequoia Capital’s Mike Dixon. Here, four of the biggest bets on the future of health insurance.