  Dark Matter (DM) is omnipresent in our universe. Despite its abundance, the
microscopic identity of DM still remains a mystery. Primordial black holes
(PBHs), possibly formed via gravitational collapse of large density
perturbations in the early universe, are one of the earliest proposed and
viable DM candidates. Recent studies indicate that PBHs can make up a large or
even entire fraction of the DM density for a wide range of masses. Here, we
briefly review the observational constraints on PBHs as DM, concentrating on
the ultra-light mass window. Ultra-light PBHs emit particles via Hawking
radiation and can be probed by observing such Hawking evaporated particles in
various space as well as ground based detectors. We also outline how
next-generation gamma ray telescopes can set a stringent exclusion limit on
ultra-light PBH DM by probing low energy photons.
