Headquarters: San Francisco, California
Year founded: 2009
Why it's revolutionary: The trendiest new clothes are often old clothes these days, and ThredUP is making trendy old clothes more accessible to shoppers. Experts predict that online resale will grow up to 10 to 15 times faster than fast fashion in the future. ThredUP has taken the charm of a thrift store treasure hunt and scaled it for an online community of thousands of shoppers. Poshmark, founded in 2011, provides a similar resale platform, while The RealReal, also founded in 2011, is a comparable platform for the luxury market.