1. P. Müller and R. Kern, contribution to the present issue.
2. M.-C. Desjonquères and D. Spanjaard, contribution to the present issue.
3. L. Kubin, contribution to the present issue.
4. Concepts in Surface Physics;Desjonquères,1993-1996
5. Theoretical, Numerical and Experimental Approaches for Structural Studies of Grain Boundaries: Methods, Remarkable Results and Perspectives