  Disorder in Weyl semimetals and superconductors is surprisingly subtle,
attracting attention and competing theories in recent years. In this brief
review, we discuss the current theoretical understanding of the effects of
short-ranged, quenched disorder on the low energy-properties of
three-dimensional, topological Weyl semimetals and superconductors. We focus on
the role of non-perturbative rare region effects on destabilizing the semimetal
phase and rounding the expected semimetal-to-diffusive metal transition into a
cross over. Furthermore, the consequences of disorder on the resulting nature
of excitations, transport, and topology are reviewed. New results on a
bipartite random hopping model are presented that confirm previous results in a
$p+ip$ Weyl superconductor, demonstrating that particle-hole symmetry is
insufficient to help stabilize the Weyl semimetal phase in the presence of
disorder. The nature of the avoided transition in a model for a single Weyl
cone in the continuum is discussed. We close with a discussion of open
questions and future directions.
