\usepackage{ifxetex}

\ifxetex
    \usepackage{fontspec} % Font selection for XeLaTeX; see fontspec.pdf for documentation
    \defaultfontfeatures{Mapping=tex-text} % to support TeX conventions like ``---''
    \usepackage{xunicode} % Unicode support for LaTeX character names (accents, European chars, etc)
    \usepackage{xltxtra} % Extra customizations for XeLaTeX
\else
    \usepackage[T1]{fontenc}
   \usepackage[utf8]{inputenc}
\fi