Abundance patterns and the chemical enrichment of nearby dwarf galaxies

As the least massive galaxies we know, dwarf spheroidal galaxies (dSph) allow to probe chemical enrichement on the smallest scales, and perhaps in its simplest expression. Particularly interesting are the issues concerning the efficency with which metals are retained or lost in these shallow potential wells (supernovae feedback), and the effect of this on star formation itself. Another fundamental issue concerns the earliest epochs of star formation: are first stars formed in similar ways and proportions in all halos ? Finally, as the smallest galaxies know, dSph have been suggested to be the surviving cousins of galaxy building blocs that (in A-CDM) assemble to make larger galaxies. This parenthood would not necessarily hold at all late times, when survivors have lived their own differentiated life, but is expected at least at the earliest epochs.I review here the chemical abundances of individual stars in the nearest dwarf spheroidal galaxies, that have become available in increasing numbers (sample size and galaxies probed) in the last decade. Special emphasis is given to: a) recent results obtain with FLAMES on VLT, highlighting the power of detailed chemical abundance patterns of large samples of stars to unravel the various evolutionnary paths followed by dSph; b) the oldest and most metal-poor populations in dSph.