  We present a general discussion of radiative four--meson processes to
$O(p^4)$ in chiral perturbation theory. We propose a definition of
``generalized bremsstrahlung'' that takes full advantage of experimental
information on the corresponding non--radiative process. We also derive general
formulae for one--loop amplitudes which can be applied, for instance, to $\eta
\ra 3\pi\gamma$, $\pi \pi \ra \pi \pi \gamma$ and $K \ra 3\pi\gamma$.
