  Radio-loud Narrow-line Seyfert 1 (NLS1) galaxies are unique probes of the
formation of powerful radio jets at extreme (near-Eddington) accretion rates
and low black hole masses, in a regime very different from classical blazars
and, therefore, not probed before. Further, strong thermal and non-thermal
components simultaneously present in their spectral energy distributions
(SEDs), shed new light on the jet-disk connection at much shorter timescales,
given their low SMBH masses. While NLS1 galaxies have been studied thoroughly
at optical and X-ray energies for decades, the populations of radio-loud, and
gamma-ray emitting NLS1 galaxies have only emerged more recently. This
contribution provides a short review of the multi-wavelength properties of this
intriguing class of Active Galactic Nuclei (AGN), including X-ray variability
and emission mechanisms, gamma-ray discoveries, SEDs, star formation activity,
host galaxy morphologies, different methods of black hole mass estimation,
(unexpected) FeII properties, and high-velocity large-scale outflows possibly
driven by the radio jet and with a surprisingly pronounced ionization
stratification.
