  We present the "endpoint" formalism for the calculation of electromagnetic
radiation and illustrate its applications in astroparticle physics. We use the
formalism to explain why the coherent radiation from the Askaryan effect is not
in general Cherenkov radiation, as the emission directly results from the
time-variation of the net charge in the particle shower. Secondly, we
illustrate how the formalism has been applied in the air shower radio emission
code REAS3 to unify the microscopic and macroscopic views of radio emission
from extensive air showers. Indeed, the formalism is completely universal and
particularly well-suited for implementation in Monte Carlo codes in the time-
and frequency-domains. It easily reproduces well-known "classical mechanisms"
such as synchrotron radiation, Vavilov-Cherenkov radiation and transition
radiation in the adequate limits, but has the advantage that it continues to
work in realistic, complex situations, where the "classical mechanisms" tend to
no longer apply and adhering to them can result in misleading interpretations.
