Manis has developed a
valuation theory on commutative rings with unity producing valuation rings which
are not integral domains. Griffin has used the valuation theory of Manis to extend
the notion of Prüfer domains to rings with zero divisors, obtaining what Griffin calls
Prüfer rings. In this paper, properties of overrings of Prüfer and valuation rings are
discussed. An example is given to show that valuation rings need not be Prüfer
rings. It is shown that every overring of a Prüfer valuation ring is a valuation
ring.