We live in a hostile world. Our cells and tissues provide a rich environment for a multitude of infectious agents which are kept at bay only as long as we maintain an effective defence system. The study of the nature and regulation of this defence consti-tutes the field of immunology. Many pathologies involve the immune system either directly or indirectly, and often their treatments are also immune-based. Furthermore, the basic unit of immune function, the lymphocyte, is arguably the most well-studied of eukaryotic cells. Thus immunology is at the centre of biomedical science.

And yet it is a peculiarly inaccessible field. Historically, immunology has relied on concepts to rationalize the great complexity of responses. Although immunologists are eager to revise their approximations in the light of new data, this ever-changing landscape makes it difficult for non-experts to identify exactly where the field stands at any given time. We predict a growing appreciation of the subject as the molecular basis of immunological con-cepts become more clearly defined.

This special collection of immunology papers, all of which have appeared in our pages in 1999, presents the breadth of the field, and we are very pleased to acknowledge Biogen, whose financial support has helped to make this supplement possible. Indeed, Nature has published many of the landmark studies over the past 40 years and we aim to continue to be at the forefront. This collection emphasizes our commitment. But it also marks a growing commitment by the Nature Publishing Group as a whole, which has made the decision to launch a new monthly journal, Nature Immunology. Readers of Nature will be kept abreast of our plans in that direction. We hope that you find the papers in this supplement to be a stimulating appetizer for more top-quality immunology that Nature looks forward to publishing in the future.

Philip Campbell Editor, Nature Ursula Weiss Senior Editor

Editor, Nature: Philip Campbell Supplement Editor: Ursula Weiss Production Editor: Simon Gribbin Art Editor: Majo Xeridat Layout: Nicola Barker Production Manager: Yvonne Strong Publisher: Liz Allen