Fused filament fabrication (FFF) is a popular additive manufacturing (AM) method which is mostly used in prototyping and in desktop 3D-printers. The widespread use in industry is obstructed by a lack of available materials, more specifically polymer materials with good mechanical properties and a good processability thereof. While high-strength polymers and composites are available and theoretically processable with FFF, easy processability is being held back by a lack of fundamental knowledge about the materials behaviour during the extrusion and deposition. In turn, this makes the determination of optimal printing parameters a very time and cost intensive trial and error process. Moreover, once optimal parameters are found they are not always transferable to other equipment since the parameters intrinsic to the machine are also detrimental in parameter determination. It is known that the flow in the nozzle and subsequent material deposition are key in the final product’s dimensional accuracy and overall strength, but the underlying process remains mainly unknown. This PhD project aims to uncover this by describing the FFF process in its four main zones and by multidimensional computer modelling and experimental validation. The model will then be used to simulate the influence of the different parameters and develop a screening method which can be used to determine optimal printing parameters considering material properties and equipment design.