Quasars, powered by accretion onto the super-massive black holes at their galaxies' centres, are capable of ejecting highly energetic outflows of gas, which can suppress star formation in the host galaxy, thereby impacting its evolution. Quasar-driven outflows are widely invoked in galaxy formation models in order to reproduce the observed properties of massive galaxies. However, there are still fundamental open questions regarding the origins of these outflows, and their relationship to accretion processes. This thesis covers a series of multi-wavelength studies of the outflow properties of quasars at redshifts 1.5 < z < 3.5 from the Sloan Digital Sky Survey. In particular, I focus on the CIV emission space which is often used to infer the strength of quasar winds via the CIV blueshift. A major aim of this thesis is to constrain the outflow properties of quasars by combining studies of emission lines, broad and narrow absorption lines.

After an introduction to quasars and their outflows, I describe my use of independent component analysis (ICA) for reconstructing the quasar spectra. With the reconstructions, I define a sample of broad absorption line (BAL) quasars, named for the presence of broad absorption lines in their spectra.

I subsequently explore the outflow properties, evident both in absorption and emission, of the high-ionisation BAL and non-BAL quasars, revealing strong systematic correlations between the emission and absorption properties. I also demonstrate that (high-ionisation) BALs and non-BALs likely represent different views of the same underlying quasar population by revealing similarities in the luminosities and emission-line outflow properties between the BAL and non-BAL quasar populations.

I investigate the prevalence of associated and outflowing narrow CIV absorption lines (NALs) in quasars across the CIV emission space. I find that the velocity of the outflowing NALs increases with CIV emission-line outflow velocity in BAL and non-BAL quasars alike. I use this result to further argue that BAL and non-BAL quasars arise from the same parent population. The velocity of line-locked systems, which are evidence for radiation line-driving, is also shown to increase as the CIV blueshift increases in BAL and non-BAL quasars which indicates the importance of radiation line-driving for driving outflows in both quasar populations.

Finally, I present an investigation of the low-frequency radio and ultraviolet properties. I find quasars with similar ultraviolet properties but differing radio properties suggesting, perhaps, that the radio and ultraviolet emission is tracing activity occurring on different time-scales. Additionally, opposing trends are observed between the radio-detection and radio-loud fractions as functions of CIV blueshift which alludes to multiple processes contributing to the radio emission. I explore the plausibility of winds, compact jets, and star formation as sources of the radio-quiet emission, ruling out none.