Clifford’s ‘*geometric algebra*‘ is presented as the natural language for expressing geometrical ideas in mathematical physics. Its spacetime version ‘*spacetime algebra*‘ is introduced and is shown to provide a powerful, invariant description of relativistic physics. Applications to electromagnetism and gravitation are discussed.

S. F. Gull, A. N. Lasenby and C. J. L. Doran, **Geometric algebra, spacetime physics and gravitation, **In O. Lahav, E. Terlevich and R. J. Terlevich, editors, *Gravitational Dynamics,* (Cambridge University Press, 1996), pp. 171-180.