Little did either suspect that five years later, they¡¦d become famous not in finance or consulting or corporate management, but at the bleeding-edge intersection of fashion and technology.

Gilt Groupe ¡V launched by Alexis, Alexandra, and three colleagues in 2007 ¡V is one of the most fascinating startups of recent years, with a valuation of more than $1 billion. And it all began with one bold idea: to bring sample sales online and change the way millions shop.

As Alexis and Alexandra write about the day Gilt.com went live: ¡§We had created a website that could potentially change the rules of retail, for both shoppers and brands. If shopping was traditionally a slow, leisurely activity that might consume an entire day, it would now be competitive, addictive, urgent, thrilling¡Xa rush delivered at the same time each day. Shopping would become not just easier, but so much fun.¡¨

But turning that vision into reality wasn¡¦t easy. Designers had long controlled their own sample sales by staging them in anonymous, makeshift locations and strictly limiting invitations. Those lucky enough to hear about a Marc Jacobs or Hermˆos sample sale would drop everything and run for dramatic, fleeting bargains. Why should elite brands support a new startup trying to replicate the experience online?

And even if brands like Valentino, Christian Louboutin, and Zac Posen got on board, would shoppers embrace such a website? Would the kind of people who love high-end fashion really visit a new online sale each day? Was ¡§accessible luxury¡¨ a breakthrough id...