We dedicate this volume of survey and research articles to Jorge Sotomayor to mark his 60th birthday, celebrated on March 25, 2002. The contributors are his friends and colleagues from Brazil and abroad. Some of them were speakers at the workshop titled Qualitative Theory of Differential Equations, held in his honor on June 17-21, 2002 at the Institute for Computational and Mathematical Sciences of the University of Sao Paulo (ICMC-USP). Sotomayor s work is the line connecting these articles. Their variety and interest attest to his remarkable influence in the study of Differential Equations, Bifurcation Theory and the Nets of Classical Geometry. Their presence here and in the workshop reflects the high regard and affection that his colleagues have for him.