This book presents the state of the art in fiber formation principles, including many original and crucial yet published developments by the author. The material is presented from the theoretical side with the evidence of agreement with experiment; with a few exceptions, uncorroborated theories are omitted. Chapter headings. Introduction. Polymer as raw material. Rheology. Polymer in fiber formation. Structure of fibers. Engineering physics. Formation from solution. Process variables. Scale change of a process. Fiber properties. Processes of spunbond . Special techniques. Appendix a: numeric data.