During January 1–October 1, 2019, the Centers for Disease Control and Prevention (CDC) reported more cases of measles since 1992, and the second highest number of reported outbreaks annually since measles elimination was declared in 2000. Measles is an acute febrile rash illness with an attack rate of approximately 90% in susceptible household contacts. Domestic outbreaks can occur when travelers contract measles outside the United States and then transmit infection to unvaccinated persons they subsequently expose in the United States. Most measles patients were unvaccinated or had an unknown vaccination status. Closely related outbreaks in New York City and New York State (excluding NYC), with ongoing transmission for almost one year in large and close-knit Orthodox Jewish communities, accounted for a substantial number of cases during 2019 and threatened elimination status of measles in the United States. Collaboration between public health authorities and undervaccinated communities is essential to preventing outbreaks and limiting transmission. Rapid implementation of measles control measures and maintenance of high national vaccination coverage with measles, mumps, and rubella vaccine remain the cornerstones for preventing widespread measles transmission.