  Helium was first isolated on Earth in 1895, by Sir William Ramsey. One
hundred and one years later, it seems like a good time to review our current
theoretical understanding of the helium atom. Helium has played an important
role in the development of both quantum mechanics and of quantum field theory.
The early history of helium is sketched. Various aspects of the modern theory
are described in some detail, including (1) the computation of fine structure
to order \alpha^2 Ry and \alpha^3 Ry, (2) the decay of metastable states, and
(3) Rydberg states and long-range forces. A brief survey is made of some of the
recent work on the quantum field theory of He and He-like ions.
