  Let $V$ be a finite dimensional vector space over a field $F$ of
characteristic different from 2, and let $Q$ be a nondegenerate, symmetric,
bilinear form on $V$. Let $C\ell(V,Q)$ be the Clifford algebra determined by
$V$ and $Q$. The bilinear form $Q$ extends in a natural way to a nondegenerate,
symmetric, bilinear form $\bar{Q}$ on $C\ell(V,Q)$. Let $G$ be the group of
isometries of $C\ell(V,Q)$ relative to $\bar{Q}$, and let $LG$ be the Lie
algebra of infinitesimal isometries of $C\ell(V,Q)$ relative to $\bar{Q}$. We
derive some basic structural information about $LG$, and we compute $G$ in the
case that $F = R, V = R^{n}$ and $Q$ is positive definite on $R^{n}$. In a
sequel to this paper we determine $LG$ in the case that $F = R, V = R^{n}$ and
$Q$ is nondegenerate on $R^{n}$.
