  The current deepest radio surveys detect hundreds of sources per square
degree below 0.1mJy. There is a growing consensus that a large fraction of
these sources are dominated by star formation although the exact proportion has
been debated in the literature. However, the low luminosity of these galaxies
at most other wavelengths makes determining the nature of individual sources
difficult. If future, deeper surveys performed with the next generation of
radio instrumentation are to reap high scientific reward we need to develop
reliable methods of distinguishing between radio emission powered by active
galactic nuclei (AGN) and that powered by star formation. In particular, we
believe that such discriminations should be based on purely radio, or relative
to radio, diagnostics. These diagnostics include radio morphology, radio
spectral index, polarisation, variability, radio luminosity and flux density
ratios with non-radio wavelengths e.g. with different parts of the infrared
(IR) regime. We discuss the advantages and limitations of these various
diagnostics methods with current and future surveys. However, weeding AGN out
of deep radio surveys can already provide several insights into the star
formation at high redshift. As well as reproducing the well known rise with
redshift in the comoving star formation rate density, we also see evidence for
the continued dominance of LIRGs and ULIRGs to the total star forming budget
across redshifts 1-3. Additionally, while we see that the IR-radio relation for
star forming galaxies does hold to high redshifts (z>1) there is a mild
deviation depending on the IR waveband used and the range of IR SEDs found. We
will discuss the possible reasons behind this change in properties.
