Christer Bennewitz is Emeritus Professor of Mathematics at Lund University. He previously worked at the University of Addis Abeba in Ethiopia, at Uppsala University in Sweden and at the University of Alabama at Birmingham in the US. His work is in the field of spectral theory for ordinary differential equations, in the last 25 years or so concentrating on inverse theory for problems not accessible to the Gelfand–Levitan theory. Malcolm Brown is Professor of Computational Mathematics at Cardiff University. His work is focused on using both analytic and computational tools to get a better understanding of problems in the spectral theory of differential operators. Recently he has become interested in inverse problems, especially inverse spectral problems, and in questions of uniqueness and recovery that involve the Dirichlet-to-Neumann map. Rudi Weikard is Professor of Mathematics at the University of Alabama at Birmingham. His recent work has been concentrated on inverse spectral and scattering theory for ordinary differential equations, for example, inverse resonance problems and Dirichlet-to-Neumann maps for quantum graphs. Previously he worked on analytic properties of the KdV hierarchy and the asymptotic behavior of large quantum systems.