  Narrow Line Seyfert 1 (NLS1) galaxies are remarkable for their extreme
continuum and emission line properties which are not well understood. New
results bearing on the spectroscopic characteristics of these objects are
presented here, with the aim of establishing their typical ultraviolet and
optical spectral behavior. We employ HST observations of 22 NLS1s, which
represent a substantial improvement over previous work in terms of data quality
and sample size. High signal-to-noise NLS1 composite spectra are constructed,
allowing accurate measurements of the continuum shape and the strengths,
ratios, and widths for lines, including weak features which are barely
identifiable in other Active Galactic Nuclei (AGN) composites. We find that the
NLS1 sources have redder UV-blue continua than those typically measured in
other quasars and Seyferts. Objects with UV line absorption show redder
spectra, suggesting that dust is important in modifying the continuum shapes.
The data also permit a detailed investigation of the previously proposed link
between NLS1s and z >~ 4 quasars. Direct comparison of their composite spectra,
as well as a Principal Component Analysis, suggest that high-z QSOs do not show
a strong preference toward NLS1 behavior.
