More than half of the world's population is living in cities and the world is turning more and more urbanized. This literature review explores the ramifications of urban transformation, showing how cities take shape and impact human health in our times. While cities can offer positive opportunities, their negative impacts related to the lack of social organization, precarious urban living and working conditions, lack of governance and opportunities as well as the lack of strategies for promoting social equity tend to increase the adverse effects on the health of the urban communities. The article also advocates the study of urban health as a branch of knowledge related to public health, proposing a common conceptual model and taxonomy for urban health. Future directions for research and practice are discussed in the light of some examples from the Brazilian scientific literature.