Some health plans sold through the Affordable Care Act's (ACA) health insurance marketplaces use narrow networks of providers to control health care costs—raising objections from some consumer advocates and critics of the law. In his latest Reflecting on Health Reform blog post, Commonwealth Fund President David Blumenthal, M.D., says that narrow networks, which have actually been around for years, are the inevitable result of relying on competition to control health care costs. Before the ACA, insurers often kept prices down by limiting benefits or cherry-picking healthy customers; today they must compete on price by controlling the costs of care.