The use of hot melt extrusion (HME) to produce pharmaceutical solid dispersions utilises pharmaceutical grade polymer(s), potentially high temperatures and mechanical energy to convert a drug substance from a crystalline to an amorphous state. Process analytical technology (PAT), in general, provides numerous manufacturing advantages but those specific to HME will be highlighted. An in-line, transmission mode, Fourier transform near infrared spectroscopy (FT-NIR) and partial least squares (PLS) method was developed for real-time drug loading (% wt/wt) predictions during hot melt extrusion of a Merck product. The NIR/PLS method has been successfully used for process fault detection and real-time quality assurance via switch gate automation control; however, the focus herein will be the use of the method for process understanding with three specific examples provided.