  I present the results of first principles calculations of the electronic
structure and magnetic interactions for the recently discovered superconductor
YFe$_2$Ge$_2$ and use them to identify the nature of superconductivity and
quantum criticality in this compound. I find that the Fe $3d$ derived states
near the Fermi level show a rich structure with the presence of both linearly
dispersive and heavy bands. The Fermi surface exhibits nesting between hole and
electron sheets that manifests as a peak in the susceptibility at $(1/2,1/2)$.
I propose that the superconductivity in this compound is mediated by
antiferromagnetic spin fluctuations associated with this peak resulting in a
$s_\pm$ state similar to the previously discovered iron-based superconductors.
I also find that various magnetic orderings are almost degenerate in energy,
which indicates that the proximity to quantum criticality is due to competing
magnetic interactions.
