The following individuals served as the primary writing team for this document: This document was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Royal Society and the National Academy of Sciences. The reviewers provided comments and suggestions, but were not asked to endorse the views of the writing team, nor did they see the final draft before its release. We wish to thank the following individuals for their review of this report: Oversight of the review process was provided by representatives of the Royal Society Council (John Pethica FRS) and the NAS Council (Jeremiah Ostriker, NAS). Staff assistance was provided by Nancy F. Huddleston, Laurie Geller, Sally Tyldesley and Tracey Elliott.

Sincere thanks to the Raymond and Beverly Sackler US-UK Scientific Forum for support of this activity.