  I review the origins and development of the idea of Dyson spheres, their
purpose, their engineering, and their detectability. I explicate the ways in
which the popular imagining of them as monolithic objects would make them
dynamically unstable under gravity and radiation pressure, and mechanically
unstable to buckling. I develop a model for the radiative coupling between a
star and large amounts of material orbiting it, and connect the observational
features of a star plus Dyson sphere system to the gross radiative properties
of the sphere itself. I discuss the still-unexplored problem of the effects of
radiative feedback on the central star's structure and luminosity. Finally, I
discuss the optimal sizes of Dyson spheres under various assumptions about
their purpose as sources of low-entropy emission, dissipative work, or
computation.
