This book starts with a detailed introduction to general relativity by world expert T. Damour. It includes a review of what may lie beyond by string theorist I. Antoniadis, and collects up-to-date essays on the experimental tests of this theory. Contrary to some beliefs, general relativity is now a theory extremely well confirmed by detailed experiments, including the precise timing of the double pulsar J0737-3039 explained by M. Kramer, member of the team which discovered it in 2003, and satellite missions such as Gravity Probe B described by leading team member J. Mester. The search for detecting gravitational waves is also very much under way as reviewed by J.-Y. Vinet.