Liquid-microjet photoelectron spectroscopy provides a direct way of measuring valence electronic structure; however, its application to solutions had been hampered by a lack of detailed understanding of the experimental parameters and procedures, and the impact of inelastic scattering of low energy electrons. A major part of the work described in this thesis is the development of rigorous experimental procedures to ensure accurate and reproducible UV photoelectron spectra of liquids, described in Chapter 2. These experimental procedures were then applied to record accurate UV photoelectron spectra of liquid water, and aqueous solutions of phenol, a common biological motif, and thymine, a DNA base. These studies aimed to elucidate the electronic structure of the liquid water (Chapter 3), aqueous phenol (Chapter 4) and aqueous thymine (Chapter 5) and how indirect ionisation processes affected their ionisation pathways.