The basic problem confronting theoretical ecology (like any theoretical science) is to hypothesize structures, processes, and interactions, and to derive their consequences. We focus on ecological patterns related to individual behavior as well as population and community dynamics, starting from a conceptual basis that asks how the individual processes of foraging, birth, death, and development determine population growth, distribution, and interactions with the environment. These individual-level processes ultimately determine population increase or decline, stability or instability, persistence or extinction, and at a larger scale, the structure of entire communities. We consider cases where individuals are characterized by age, body size, developmental stages, infection status, genotype, and/or spatial location.