  Spin-squeezing is a well-established "quantum technology", where
well-designed correlations in an ensemble of two-level systems reduce the
statistical uncertainty of spectroscopic experiments. This paper reviews some
important advances in the field, with emphasis on the author's contributions
concerning in particular the fundamental limits imposed by decoherence.
Building on the material presented in the first part, new ideas and some
promising developments are outlined in the last section.
