  A Seifert bundle over a variety X is a variety Y with a proper action of the
multiplicative group such that the quotient is X. The topological version of
this notion (using circle actions) was introduced by Seifert, the holomorphic
version by Orlik and Wagreich. The aim of this paper is to provide the
foundational results for Seifert bundles over an arbitrary normal variety X.
The main results are a classification and a smoothness criterion.
