We describe the evolution of the organization of public health services in the city of Barcelona (Catalonia, Spain) until the creation of the Barcelona Public Health Agency. This Agency is a consortium created by the Barcelona City Council and the Government of Catalonia as the sole entity responsible for regional and local public health services in the city. The underlying logic for the Agency's design, as well as its mission, vision and value statements, strategy, services' portfolio, and the role of leadership in the process, are analyzed. Aspects related to the Agency's quality and communication plans, as well as the design of its processes, and its policy in terms of alliances for research and training in public health, are discussed. Finally, the main challenges for the future are described.