  An important open question today is the understanding of the relevance that
dark matter (DM) halo substructure may have for DM searches. In the standard
cosmological framework, subhalos are predicted to be largely abundant inside
larger halos, i.e., galaxies like ours, and are thought to form first and later
merge to form larger structures. Dwarf satellite galaxies -- the most massive
exponents of halo substructure in our own galaxy -- are already known to be
excellent targets and, indeed, they are constantly scrutinized by current
gamma-ray experiments in their search for DM annihilation signals. Lighter
subhalos not massive enough to have a visible baryonic counterpart may be good
targets as well given their typical number densities and distances. In
addition, the clumpy distribution of subhalos residing in larger halos may
boost the DM signals considerably. In an era in which gamma-ray experiments
possess, for the first time, the exciting potential of reaching the most
relevant regions of the DM parameter space, a profound knowledge of the DM
targets and scenarios being tested at present is mandatory if we aim for
accurate predictions of DM-induced fluxes, for investing significant telescope
observing time to selected targets, and for deriving robust conclusions from
our DM search efforts. In this regard, a precise characterization of the
statistical and structural properties of subhalos becomes critical. With the
Special Issue "The Role of Halo Substructure in Gamma-Ray Dark Matter Searches"
[https://www.mdpi.com/journal/galaxies/special_issues/Gamma-RayDMS], we aimed
to summarize where we stand today on our knowledge of the different aspects of
the DM halo substructure; to identify what are the remaining big questions, how
we could address these and, by doing so, to find new avenues for research.
