  I present a broad overview of modelling of the Narrow Line Region (NLR) of
active galaxies, and discuss some of the more recent models we currently have
for the emission from the NLR. I show why the emission line ratios from the NLR
are constrained to certain observed values, and describe what physical
parameters we can derive from observations using emission line models. Also
presented are some examples of this, looking at the metallicity and excitation
mechanism of active galaxies. As a final point, the limitations of the current
models are discussed, and how how the combination of modelling and theory can
help us solve some of the questions that still remain within the NLR.
