A scientific journal exists only because of the good will and assistance of its reviewers. We can only publish less than a fifth of the papers we receive and, in making our decisions, we depend on the expertise of many people. This year a total of 315 reviewers have helped us to decide about the papers that we should publish. Their names are listed below and we would like to take this opportunity to thank them. The list refers to reviewers assigned until the 6th December 2006.