  We review some recent results beyond the now established theory of
magnetization switching of a nanoparticle within the single-spin approximation.
The first extension is that of the Stoner-Wohlfarth model for magnetization
static switching under applied magnetic field including the effect of
temperature at long-time scales. The second concerns a generalization of the
N\'eel-Brown model for thermoactivated dynamic magnetization switching to
include the effect of exchange interaction in the framework of Langer's theory
in the intermediate-to-high damping limit. We finally argue why the single-spin
approximation is not appropriate for very small nanoparticles.
