  MOND, invented by Milgrom, is a phenomenological scheme whose basic premise
is that the visible matter distribution in a galaxy or cluster of galaxies
alone determines its dynamics. MOND fits many observations surprisingly well.
Could it be that there is no dark matter in these systems and we witness rather
a violation of Newton's universal gravity law ? If so, Einstein's general
relativity would also be violated. For long conceptual problems have prevented
construction of a consistent relativistic substitute which does not obviously
run afoul of the facts. Here I sketch TeVeS, a tensor-vector-scalar field
theory which seems to fit the bill: it has no obvious conceptual problems and
has a MOND and Newtonian limits under the proper circumstances. It also passes
the elementary solar system tests of gravity theory.
