The package provides a LaTeX interface to the micro-typographic extensions that were introduced by pdfTeX and have since also propagated to XeTeX and LuaTeX: most prominently, character protrusion and font expansion, furthermore the adjustment of interword spacing and additional kerning, as well as hyphenatable letterspacing (tracking) and the possibility to disable all or selected ligatures. These features may be applied to customisable sets of fonts, and all micro-typographic aspects of the fonts can be configured in a straight-forward and flexible way. Settings for various fonts are provided. Note that character protrusion requires pdfTeX, LuaTeX, or XeTeX. Font expansion works with pdfTeX or LuaTeX. The package will by default enable protrusion and expansion if they can safely be assumed to work. Disabling ligatures requires pdfTeX or LuaTeX, while the adjustment of interword spacing and of kerning only works with pdfTeX. Letterspacing is available with pdfTeX or LuaTeX. The alternative package `letterspace', which also works with plain TeX, provides the user commands for letterspacing only, omitting support for all other extensions.