  Dense low mass cores in nearby clouds like Taurus and Auriga are some of the
simplest sites currently forming stars like our Sun. Because of their
simplicity and proximity, dense cores offer the clearest view of the different
phases of star formation, in particular the conditions prior to the onset of
gravitational collapse. Thanks to the combined analysis of the emission from
molecular lines and the emission/absorption from dust grains, the last several
years have seen a very rapid progress in our understanding of the structure and
chemical composition of starless cores. Previous contradictions between
molecular tracers are now understood to arise from core chemical
inhomogeneities, which are caused by the selective freeze out of molecules onto
cold dust grains. The analysis of the dust emission and absorption, in
addition, has allowed us to derive accurate density profiles, and has made
finally possible to carry out self consistent modeling of the internal
structure of starless cores. In this paper I briefly review the evolution of
core studies previous to the current golden age, and show how multi-tracer
emission can now be modeled in a systematic manner. Finally I show how we can
start to reconstruct the early history of core formation taking advantage of
the chemical changes in the gas.
