This book constitutes of the major results of the EU COST (European Cooperation in the field of Scientific and Technical Research) Action 277: NSP - Nonlinear Speech Processing - running from April 2001 to June 2005. The results were presented at the last meeting of the management committee of COST Action 277, held in Heraklion, Crete, Greece on September 20-23, 2005 during the Workshop on Nonlinear Speech Processing, WNSP 2005. The 13 revised full papers in this state-of-the-art survey were carefully reviewed and selected for inclusion in the book and are preceded with an introductory leading-in by the editors. The articles present overviews of the four years research combining linear and non linear approaches for processing the speech signal. The aim of this book is to provide an additional and/or an alternative way to the traditional approach of linear speech processing and be mainly used by the researcher working in the domain. The papers cover areas such as speech analysis for speech synthesis, speech recognition, speech-non speech discrimination and voice quality assessment, speaker recognition/verification from a natural or modified speech signal, speech recognition, speech enhancement, and emotional state detection.