Two practical examples of system dynamics models in public health are introduced. The first is a national salt reduction model based on co-flows and the Bass diffusion model. It consists of the people’s awareness subsystem, people’s taste for salt subsystem, and food product subsystem. Changes in the stocks and flows of each subsystem are shown. The second is a Japanese healthcare cost model, which is based on aging chains. It optimizes the model parameters using national statistics as reference data. Changes in medical and long-term care expenditures are shown by scenario.