  After recalling why dynamical adjustment mechanisms represent a particularly
attractive possibility for solving the cosmological constant problem, we
briefly discuss their intrinsic difficulties as summarized in Weinberg's no-go
theorem. We then comment on some problems of the recently proposed
`self-tuning' mechanism in 4+1 dimensions. Finally, we describe an alternative
approach which uses the time-evolution of the universe to achieve a dynamical
relaxation of the cosmological constant to zero.
