The goal of this chapter is to introduce the reader to the importance of extrusion dies design as well as the complexities inherent in the task. Extrusion is of vital importance to all plastics processing. In addition to providing raw stock such as sheet for thermoforming and pellets for injection molding and other extrusion processing, numerous end-use products are made with extrusion such as film, tubing, and a variety of profiles. Although the types of extruded products made can differ dramatically in shape, there are a set of common rules that govern basic die design. For example, it is important to streamline the flow from the inlet to the exit, and as a practical measure, to fine-tune the flow balance and product dimensions, flow adjustment devices could be included in the die design. Several unique products are made by extrusion and the dies needed to make these products are classified as: 1) sheet dies; 2) flat-film and blown-film dies; 3) pipe and tubing dies; 4) profile extrusion dies; and 5) co-extrusion dies. Furthermore, each product type has unique hardware downstream of the die to shape and cool the extruded melt. To aid the reader, detailed illustrations of the various die designs and the complementary downstream cooling and shaping hardware are shown. Predicting the required die profile to achieve the desired product dimensions is a very complex task and requires detailed knowledge of material characteristics and flow and heat transfer phenomena, and extensive experience with extrusion processing. Extrusion die design is still more an art than a science, even though the latter is becoming more and more relevant for design optimization because of recent advancement in the powerful computation and modeling of complex flow and heat transfer processes, before, through, and after the die.