This interactive book is designed for anyone interested in polymer melt extrusion instabilities. It is aimed to serve as an introductory overview of the nonlinear phenomena observed during the extrusion of polyethylene melts. In this ebook we present optical evidence of some of the instabilities observed during the extrusion of polyethylene melts. An experimental system capable to detect these instabilities is also presented, i.e. a high sensitivity mechanical pressure instability detection system.