Rheology – not to be confused with theology – represents an important and distinctive area of modern engineering science: the ability to specify and control a material's rheology and associated microstructures is a key aspect of many process and product innovations. In the pharmaceutical sector, emulsions and the cohesive wet masses employed in extrusion processes for granulation – often called pastes – are examples of materials with complex rheological behaviour. Understanding these behaviours, being able to quantify them and then incorporating that knowledge into appropriate models will allow optimisation of steps such as process design, modelling and development, as well as improving product quality, efficiency and time of processing in manufacturing.