This thesis pursues an enhanced understanding of flow dynamics and mixing within Sulzer SMX mixers. A number of techniques were used, with the main focus on Positron Emission Particle Tracking (PEPT), as well as Particle Image Velocimetry (PIV) and high speed image capture. PEPT tracer location data was processed to derive properties such as local velocity fields, mixing efficiencies, occupancies and changeover efficiencies, for a number of model Newtonian and non-Newtonian fluids, under industrially relevant flow conditions. It was demonstrated that velocity fields within SMX mixers are not adversely affected by the fluid rheology. Comparable velocity maps were also obtained using PIV, where transparent 3D printed mixer elements were successfully used with the technique for the first time. The assessment of the mixing patterns illustrated that the concentric feed orientation offers the fastest reduction in variance across the mixer cross-section, when compared to side-by-side feed patterns. Analysis of occupancies demonstrated a sharp breakthrough front, reminiscent of plug flow, while the assessment of the changeover patterns further emphasised the resemblance to plug flow within the mixer. A model was derived predicting the time required to achieve a desired level of changeover within a system with known rheological properties and geometry.