The supposed benefits of e-cigarettes are front and center today, with news that the FDA will propose new rules for regulating the devices. At stake is the future of an industry already generating $2 billion in revenue in the U.S., and expected to grow dramatically, perhaps even outstripping the market for traditional cigarettes. But is this new market a replacement for the existing cigarette market, or is it creating new demand? The former would likely mean a substantial improvement in public health; the latter would mean a steep increase in nicotine addiction.