A tribute [Into. to special issue deicated to Balthasar van der Pol]

The Guest Editors dedicate this Special Issue of the IRE Transactions on Circuit Theory to the memory of Professor Balthasar van der Pol, on behalf of the Institute of Radio Engineers (IRE) and the International Scientific Radio Union (ISRU). The issue brings together, by invitation, contributions from outstanding scientists throughout the world, a fitting memorial to a scientist, engineer, and educator of the stature of Prof. van der Pol, who made so many contributions not only to science, engineering and education, but also to international scientific cooperation. It is their hope that this publication will serve to give an impetus to the extension of circuit theoretic concepts and viewpoints to nonlinear systems, and thus contribute to the aims visualized by Prof. van der Pol.