Around 150 cities have emerged as notable at a global scale. With a global population of fewer than 12%, they generate 46% of world gross domestic product. There is growing interest in how cities can accelerate health improvements through wider social and economic collaboration. A team led by Public Health England in London visited counterparts in New York City and Paris to examine how city health leaders addressed public health challenges. The three cities have similar health challenges but different legal, political and fiscal resources for promoting and protecting health. Consequently, there is no single model that every city could adopt. Organizational structures, interpersonal relationships and individual skills can play an important part in effective delivery of better city health. Lack of access to published evidence on how practice has been influenced by city health policies hampers learning between cities. There is little easily comparable data to guide those interested in such learning. Municipal governments are ideally situated to join researchers to fill this gap in the literature.