  Narrow line Seyfert 1 (NLSy1) galaxies constitute a class of active galactic
nuclei characterized by the full width at half maximum (FWHM) of the H$\beta$
broad emission line < 2000 km/s and the flux ratio of [O III] to H$\beta$ < 3.
Their properties are not well understood since only a few NLSy1 galaxies were
known earlier. We have studied various properties of NLSy1 galaxies using an
enlarged sample and compared them with the conventional broad-line Seyfert 1
(BLSy1) galaxies. Both the sample of sources have z $\le$ 0.8 and their optical
spectra from SDSS-DR12 that are used to derive various physical parameters have
a median signal to noise (S/N) ratio >10 per pixel. Strong correlations between
the H$\beta$ and H$\alpha$ emission lines are found both in the FWHM and flux.
The nuclear continuum luminosity is found to be strongly correlated with the
luminosity of H$\beta$, H$\alpha$ and [O III] emission lines. The black hole
mass in NLSy1 galaxies is lower compared to their broad line counterparts.
Compared to BLSy1 galaxies, NLSy1 galaxies have a stronger FeII emission and a
higher Eddington ratio that place them in the extreme upper right corner of the
$R_{4570}$ - $\xi_{Edd}$ diagram. The distribution of the radio-loudness
parameter (R) in NLSy1 galaxies drops rapidly at R > 10 compared to the BLSy1
galaxies that have powerful radio jets. The soft X-ray photon index in NLSy1
galaxies is on average higher (2.9 $\pm$ 0.9) than BLSy1 galaxies (2.4 $\pm$
0.8). It is anti-correlated with the H$\beta$ width but correlated with the Fe
II strength. NLSy1 galaxies on average have a lower amplitude of optical
variability compared to their broad lines counterparts. These results suggest
Eddington ratio as the main parameter that drives optical variability in these
sources.
