Concentration has been in the areas of high-intensity collective effects and machine coupling impedance, with the goal of improving the performance of particle accelerators. Another major research thrust has been the electron cloud effect, a growing concern in high-intensity, high-energy rings. Long-term research interests include: storage-ring FELs, coherent synchrotron radiation and nonlinear effects in beams, and plasma-based light sources. Electron cloud studies have lead to collaborations at LANL, LBNL, SLAC, SNS, IHEP (China), and Cornell.