  In the last few years, interest in radio detection of cosmic ray air showers
has risen continuously. By now, large-scale application of the radio technique
is under investigation in the framework of LOFAR and the Pierre Auger
Observatory. The experimental efforts are accompanied by new approaches to
describe and model the underlying radiation mechanisms, to lay the foundation
for an interpretation of the experimental data. In this article, I review the
current radio emission theory and simulations, with slight focus on the
geosynchrotron model and its predictions for the information content of the
radio signals.
