In the second annual Disruptor 50 list, CNBC features private companies in 27 industries—from aerospace to enterprise software to retail—whose innovations are revolutionizing the business landscape. These forward-thinking upstarts have identified unexploited niches in the marketplace that have the potential to become billion-dollar businesses, and they rushed to fill them. In the process, they are creating new ecosystems for their products and services. Unseating corporate giants is no easy feat. But we ranked those venture capital–backed companies doing the best job. Already it’s hard to think of the world without them. Read more about the list ranking and the methodology.