  A simple description of the vacuum energy (cosmological constant) problem for
non-experts is presented. Basic features of cosmology with non-zero vacuum
energy are discussed. The astronomical data which indicate that the universe is
filled with an anti-gravitating state of matter are described. The mechanisms
which may lead to cancellation of almost infinite vacuum energy down to the
astronomically observed value are discussed. The idea of dynamical adjustment
is considered in some more detail.
