What’s a cloud services broker, and why do you need one?

The proportion of cloud services purchased through cloud brokers is growing, and Gartner predicts it will soon make up a substantial portion of cloud purchases. The appeal of a cloud broker is obvious: It allows the enterprise to leverage specialized expertise to provision expensive and complicated services. But what is a cloud services broker (CSB), and why do so many companies need one? What’s the impact of CSBs on IT, and should brokering the cloud be done externally or can it be as an internal IT function?