Thermohaline intrusions are produced by lateral shear advection across thermal and haline fronts, self-driven via double-diffusion, and cause significant lateral fluxes. The primary goal of this thesis is to understand the mechanisms responsible for their development and equilibration. Previous theories (mean-field models) were limited by their reliance on the vertical flux laws, which still remain a great source of uncertainty and require modelers to assume that intrusion development is uniquely ...