  We study $C^*$-algebras arising from $C^*$-correspondences, which was
introduced by the author. We prove the gauge-invariant uniqueness theorem, and
obtain conditions for our $C^*$-algebras to be nuclear, exact, or satisfy the
Universal Coefficient Theorem. We also obtain a 6-term exact sequence of
$K$-groups involving the $K$-groups of our $C^*$-algebras.
