Extrusion is the most fundamental method of processing of polymeric materials and it is involved in the production of commodities in diverse industrial sectors. Obviously, the thermal homogeneity of the process melt output presents a major challenge for high quality extruded products. However, the effective thermal monitoring and control still remains an issue despite the significant developments to the process over the last few decades. Therefore, the major aim of this book is to provide an extensive knowledge to the reader in the area of process thermal measurements (e.g. present thermal monitoring techniques, previous attempts on thermal monitoring, difficulties/challenges for accurate thermal measurements, areas on which further research should be carried out) in polymer extrusion. Moreover, this book will provide a good description on the basic process mechanisms in polymer extrusion while offering a large number of references for further reading of the interested parties. Basically, this book was written for the use of both industrial and academic users and hence both the theoretical and experimental information are presented for the better understanding of any reader.