  The emission properties of atoms lie at the foundations of both quantum
theory and light-matter interactions. In the context of macroscopic media,
exact knowledge thereof is important both in current quantum technologies as
well as in fundamental studies. While for isotropic media, this is a very
well-studied problem, there are still big gaps in the theory of anisotropic
media. In particular, to the best of our knowledge, an explicit expression for
the spontaneous emission rate in general anisotropic media has not been
presented. In this work, we first derive the quantised electromagnetic field
operators to calculate the emission rate in uniaxial media. For the more
general case of biaxial media we propose an approximate expression based on
interpolation between the limiting cases of uniaxial media. We support our
model with numerical simulations which are in strong agreement for typical
media configurations, and furthermore show how local field effects can be taken
into account in the model.
