  The UV spectral range (1100 - 3000 A) contains the strongest resonance lines
observed in active galactic nuclei (AGN). Analysis of UV line intensity ratios
and profile shapes in quasar spectra provide diagnostics of physical and
dynamical conditions in the broad line emitting region. This paper discusses
properties of UV lines in type-1 AGN spectra, and how they lead an estimate of
ionizing photon flux, chemical abundances, radius of the broad line emitting
region and central black hole mass. These estimates are meaningfully
contextualised through the 4D "eigenvector-1" (4DE1) formalism.
