I present a proof of Kirchberg’s classification theorem: two separable, nuclear,
O
∞
\mathcal O_\infty
-stable
C
∗
C^\ast
-algebras are stably isomorphic if and only if they are ideal-related
K
K
KK
-equivalent. In particular, this provides a more elementary proof of the Kirchberg–Phillips theorem which is isolated in the paper to increase readability of this important special case.