The question of a possible temporal variation of the fundamental constants was raised by Paul
Dirac in his large number hypothesis in 1937. Today it appears in the context of the search for
a unified theory of the fundamental interactions. It touches both fundamental and applied
physics as the postulate of the unalterability of the constants is the foundation for modern
metrology. The book presents reviews written by leading experts in the field. Focussing on the
question of variations of the fundamental constants in time or space the chapters cover the
theoretical framework in which variations are expected and the search for variations of
quantities like the fine-structure constant the electron proton mass ratio g-factors of
proton and neutron etc. in astrophysical and geophysical observations and in precision
experiments with atomic clocks and frequency standards.
