  We discuss several sets of Ti II absorption-line data, which probe a variety
of interstellar environments in our Galaxy and in the Magellanic Clouds.
Comparisons of high-resolution (FWHM ~ 1.3-1.5 km/s) Ti II spectra of Galactic
targets with corresponding high-resolution spectra of Na I, K I, and Ca II
reveal both similarities and differences in the detailed structure of the
absorption-line profiles -- reflecting component-to-component differences in
the ionization and depletion behaviour of those species. Moderate-resolution
(FWHM ~ 3.4-4.5 km/s) spectra of more heavily reddened Galactic stars provide
more extensive information on the titanium depletion in colder, denser clouds
-- where more than 99.9 per cent of the Ti may be in the dust phase.
Moderate-resolution (FWHM ~ 4.5-8.7 km/s) spectra of stars in the Magellanic
Clouds suggest that the titanium depletion is generally much less severe in the
LMC and SMC than in our Galaxy [for a given N(H_tot), E(B-V), or molecular
fraction f(H_2)] -- providing additional evidence for differences in depletion
patterns in those two lower-metallicity galaxies. We briefly discuss possible
implications of these results for the interpretation of gas-phase abundances in
QSO absorption-line systems and of variations in the D/H ratio in the local
Galactic ISM.
