Why is the universe so symmetrical? / Dennis Sciama -- Null congruences and Plebanski-Schild spaces / Ivor Robinson -- Linearization stability / Dieter Brill -- Nonlinear model field theories based on harmonic mappings / Charles W. Misner -- Gravitational fields in general relativity / Roy F. Kerr -- On the potential barriers surrounding the Schwarzschild black hole / S. Chandrasekhar -- The initial value problem and beyond / James W. York, Jr. and Tsvi Piran.