Just when you thought you finally understood health insurance exchanges, Commonwealth Fund President David Blumenthal, M.D., says in his latest Reflecting on Health Reform blog post, along comes a curveball: private exchanges. In addition to state and federally run public exchanges, there are private exchanges that sell health insurance online to employers. For brokers, consultants, and insurers, private exchanges can provide a way to hold on to existing clients by offering a product that looks a lot like what the public exchanges are offering.