  (Abridged) The discovery of extrasolar planetary systems revealed an
unexpected diversity of planetary systems that has revolutionized planet
formation theory. A strong program of theoretical research is essential to
maximize both the discovery potential and the scientific returns of future
observational programs, so as to achieve a deeper understanding of the
formation and evolution of planetary systems. We outline three broad categories
of theoretical research: detailed studies of specific planetary systems,
testing planet formation models by comparing their predictions to the observed
exoplanet population, and detailed modeling of specific physical processes. We
describe how such theoretical research plays an important role in analyzing
observations for a wide range detection methods and contributes to
understanding the Earth's place in the universe and the potential for
Earth-like life beyond our solar system. In this white paper, we suggest how to
maximize the scientific return of future exoplanet observations. Our
recommendations include a strong theory program, support for multiple
observational programs that will study a diverse set of planets and stars,
significant observing time devoted to follow-up observations, and healthy
collaboration between observers and theorists.
