E-cigarettes—small devices which deliver vaporized nicotine to users—are a $2 billion industry. The three large tobacco companies have also made forays into the market. While regulators study the health impacts and safety of e-cigarettes, the demand for the product continues to grow. E-cigarettes are not subject to New York City bans on smoking in public parks or beaches, and it’s not uncommon to see users “vaping” in restaurants, subways and theaters. Dr. Richard Hurt, director of the Nicotine Dependence Center at the Mayo Clinic, and Dr. Deepak Saxena, assistant professor of basic science and craniofacial biology at the NYU College of Dentistry, talk about how e-cigarettes work and their growing popularity.