This thesis is focused on demonstrating advancements and potentials of the time-resolved second harmonic generation technique applied to the characterization of ultrafast photoinduced processes at liquid interfaces. In particular, it presents the work up to date, which has been conducted along three different strands: (1) Excited-state dynamics and spectroscopic signatures of interfacial molecular probes (e.g. organic dyes); (2) Characterization of environmental properties in interfacial systems; (3) Photoinduced electron transfer at/through liquid/liquid interface.