  Extensive air shower (EAS) arrays directly sample the shower particles that
reach the observation altitude. They are wide field of view (FoV) detectors
able to view the whole sky simultaneously and continuously. In fact, EAS arrays
have an effective FoV of about 2 sr and operate with a duty cycle of
$\sim$100\%. This capability makes them well suited to study extended sources,
such as the Galactic diffuse emission and measure the spectra of Galactic
sources at the highest energies (near or beyond 100 TeV). Their sensitivity in
the sub-TeV/TeV energy domain cannot compete with that of Cherenkov telescopes,
but the wide FoV is ideal to perform unbiased sky surveys, discover transients
or explosive events (GRBs) and monitor variable or flaring sources such as
Active Galactic Nuclei (AGN). An EAS array is able to detect at the same time
events induced by photons and charged cosmic rays, thus studying the connection
between these two messengers of the non-thermal Universe. Therefore, these
detectors are, by definition, multi-messenger instruments.
  Wide FoV telescopes are crucial for a multi-messenger study of the
Gravitational Wave events due to their capability to survey simultaneously all
the large sky regions identified by LIGO and VIRGO, looking for a possible
correlated $\gamma$-ray emission.
  In this contribution we summarize the scientific motivations which push the
construction of new wide FoV air shower detectors and introduce the future
instruments currently under installation. Finally, we emphasize the need of an
EAS array in the Southern hemisphere to monitor the Inner Galaxy and face a
number of important open problems.
