This 4-week Summer School Workshop, the third in a series devoted to comparisons of marine, terrestrial and freshwater ecosystems, focuses on structured population models. Structured models explicitly link the biology of individual to the dynamics of populations. The course will cover all three main mathematical approaches to structured models: matrix population models, partial differential equation models, and delay differential equation models. Structured models have a crucial role to play in two important problems that cut across marine, terrestrial and freshwater ecosystems. One is the response of populations to global climate change, and the other is the difference between marine populations and terrestrial populations. This course is designed to examine in which way individual responses in different environments are translated into population dynamics.