  The developable surface is an important surface in computer aided design,
geometric modeling and industrial manufactory. It is often given in the stan-
dard parametric form, but it can also be in the implicit form which is commonly
used in algebraic geometry. Not all algebraic developable surfaces have
rational parametrizations. In this paper, we focus on the rational developable
surfaces. For a given algebraic surface, we first determine whether it is
developable by geometric inspection, and we give a rational proper
parametrization for the af- firmative case. For a rational parametric surface,
we can also determine the developability and give a proper reparametrization
for the developable surface.
