This volume contain thirty-one papers based on talks delivered at the 4th Workshop of the Nonlinear Control Network (http://www.shef/?NCN4), held at The University of She?eld, 25-28 June, 2001. We would like to emphasize one peculiarity of our ?eld: nonlinear control is an example of a theory situated at a crossroad between mathematics and engineering science. Due to this position, nonlinear control has its roots in both ?elds and, as we deeply believe, can bring new ideas and new results for both domains. The book re?ects very well this "double character" of nonlinear control theory: the reader will ?nd in it results which cover a wide varietyofproblems:startingfrompuremathematics,throughitsapplications to nonlinear feedback design, and all the way to recent industrial advances. The following delivered invited talks at the Workshop : Frank Allgower, Alessandro Astol?, Riccardo Marino Francoise Lamnabhi-Lagarrigue, Wei Lin and Malcolm Smith Altogether the book contains 31 papers and therefore it is impossible to mention here all the discussed topics.