  Let $S$ be a commutative ring with identity and $R$ a unitary subring of $S$.
An ideal $I$ of $S$ is called an $R$-conductor ideal of $S$ if $I=\{x\in S\mid
xS\subseteq V\}$ for some intermediate ring $V$ of $R$ and $S$. In this note we
present necessary and sufficient criterions for being an $R$-conductor ideal of
$S$. We generalize several well known facts about them and present a simple
approach to rediscover the results of both old and recent papers. We sketch the
boundaries of our criterions by providing a few counterexamples.
