Let $K$ denote a field and let $V$ denote a vector space over $K$ with finite
positive dimension. We consider an ordered pair of linear transformations
$A:V\to V$ and $A^*:V\to V$ that satisfy conditions (i), (ii) below.
(i) There exists a basis for $V$ with respect to which the matrix
representing $A$ is irreducible tridiagonal and the matrix representing $A^*$
is diagonal.
(ii) There exists a basis for $V$ with respect to which the matrix
representing $A$ is diagonal and the matrix representing $A^*$ is irreducible
tridiagonal.
We call such a pair a {\it Leonard pair} on $V$. We discuss a correspondence
between Leonard pairs and a class of orthogonal polynomials consisting of the
$q$-Racah polynomials and some related polynomials of the Askey scheme. For the
polynomials in this class we obtain the 3-term recurrence, difference equation,
Askey-Wilson duality, and orthogonality in a uniform manner using the
corresponding Leonard pair.