This supplement of the Journal of American Society of Nephrology contains some of the proceedings of the Fifth International Conference on Hypertension and the Kidney. The Conference, held in Madrid, Spain, in February 2006, was organized by the Department of Nephrology of the Hospital General, Universitario Gregorio Marañón, under the sponsorship of the Universidad Complutense de Madrid, Spanish Society of Nephrology, Spanish Society of Hypertension, and European Renal Association-European Dialysis and Transplant Association.