This is a brief introduction to general relativity, designed for both
students and teachers of the subject. While there are many excellent
expositions of general relativity, few adequately explain the
geometrical meaning of the basic equation of the theory: Einstein's
equation. Here we give a simple formulation of this equation in terms
of the motion of freely falling test particles. We also sketch some
of the consequences of this formulation and explain how it is
equivalent to the usual one in terms of tensors. Finally, we include
an annotated bibliography of books, articles and websites suitable for
the student of relativity.