In both the present volume of Advances in Nuclear Physics and in the next volume, which will follow in a few months' time, we have stretched our normal pattern of reviews by including articles of more major proportions than any we have published before. As a result we have only three review articles in Volume 5. From the beginning of this series it has been our aim, as editors, to achieve variation in the scope, style, and length of individual articles sufficient to match the needs of the individual topic, rather than to restrain authors within rigid limits. It has not been our experience that this flexibility has led to unnecessary exuberance on the part of the authors. We feel that the major articles now entering the series are entirely justified. The article by Professor Delves on "Variational Techniques in the Nuclear Three-Body Problem" is an authoritative, definitive article on a subject which forms a cornerstone of nuclear physics. If we start with two body interactions, then the three-nucleon system is, perhaps, the only many nucleon system whose exact description may lie within the scope of human ingenuity. In recent years some new techniques of scattering theory, origi nating mostly in particle physics, have led to a great deal of new interest in the nuclear three-body problem. In this series we have had two articles (by Mitra and by Duck) on the new approaches.

Inhalt
1 Variational Techniques in the Nuclear Three-Body Problem.- 1. Introduction.- 2. Variation Principles for Bound States.- 3. Numerical Techniques.- 4. Bound State Calculations with Realistic Local Potentials.- 5. Variational Methods for Scattering States.- 6. Variational Methods for the Faddeev Equations.- 7. Summing Up.- Acknowledgments.- Appendix A.- References.- 2 Nuclear Matter Calculations.- 1. Introduction.- 2. Calculation of the G Matrix.- 3. Comparison of Methods for Constructing the G Matrix.- 4. Results of Calculations for Realistic Forces.- 5. Additional Considerations.- 6. Higher-Order Cluster Contributions.- 7. Toward Finite Nuclei.- 8. Conclusion.- References.- 3 Clustering in Light Nuclei.- 1. Introduction.- 2. Shell Model and Deformed Hartree-Fock Model.- 3. Weak Coupling Model and Quartet States.- 4. Cluster Model.- 5. Individual Nuclei.- 6. Electromagnetic Properties and Form Factors for Electron Scattering.- 7. Comparison Between Models in the Normal Shell Model States.- 8. Effect of the Spin-Orbit Interaction and Hybridization.- 9. Exotic States and Alpha Particle Widths.- 10. Discussion and Possible Further Developments.- Appendix: Matrix Elements Between Two Brink Wave Functions.- References.