This book presents an overview of the current understanding of gravitation with a focus on the
current efforts to test its theory especially general relativity. It shows how the quest for a
deeper theory which would possibly incorporate gravity in the quantum realm is more than ever
an open field.The majority of the contributions deals with the manifold facets of experimental
gravitation but the book goes beyond this and covers a broad range of subjects from the
foundations of gravitational theories to astrophysics and cosmology.The book is divided into
three parts. The first part deals with foundations and Solar System tests. An introductory
pedagogical chapter reviews first Newtonian gravitational theory special relativity the
equivalence principle and the basics of general relativity. Then it focuses on approximation
methods mainly the post-Newtonian formalism and the relaxed Einstein equations with a
discussion on how they are used in treating experimental tests and in the problem of generation
and detection of gravitational waves. Following this is a set of chapters describing the most
recent experiments techniques and observations on the testing of gravity theories in the
laboratory around the Earth and in the Solar System.The second part is dedicated to
astrophysical topics deeply linked with the study of gravitation namely binary pulsars and the
perspective of direct detection of gravitational waves. These cases are paradigmatic in that
the gravitational signals act at the same time as messengers helping us to understand the
properties of important and wide classes of astrophysical objects.The third part explores the
many open issues in current knowledge of gravitation machinery especially related to
astrophysical and cosmological problems and the way possible solutions to them impact the quest
for a quantum theory of gravitation and unified theory. Included is a selection of the many
possiblepaths giving a hint to the subtleties one is called upon. Whenever possible a close
link to observational constraints and possible experimental tests is provided.In selecting the
topics of the various contributions particular care has been devoted to ensure their fit in a
coherent representation of our understanding of gravitational phenomena. The book is aimed at
graduate level students and will form a valuable reference for those working in the field.
