Hyphenation in Beamer Presentations

Actually, beamer doesn't disable hyphenation. However, as \raggedright instead of justified text is used, hyphenation becomes nearly impossible. You can use the ragged2e package which provides the \RaggedRight macro to get better results:

\documentclass{beamer}
\usepackage{ragged2e}
\let\raggedright=\RaggedRight
\usepackage{kantlipsum} % only used to generate dummy text
\begin{document}
\begin{frame}
\begin{itemize}
\item \kant[1]
\end{itemize}
\end{frame}
\end{document}

Compare the output of \raggedright and \RaggedRight:

Still, I totally agree with the comments you already received: If you actually need automatic hyphenation, you should probably think about reducing the amount of text on your slides!

In some languages you will have really long words. So reducing the number of words as suggested in some comments is simply not possible. You can set a parbox around your text to get hyphenation working. e.g.:

\parbox{\linewidth}{text with possible long words to hyphenate}

Here is a fully working example using \hy{text} as a helper for reusing command several times:

\documentclass{beamer}
\usepackage[ngerman]{babel} % example language with long words                                                                                                                                                                                
\def\hy#1{\parbox{\linewidth}{#1}} % helper for using command several times                                                                                                                                                                   
\begin{document}
\begin{frame}
  \hy{Die Speicherverwaltungsadressen der heutigen
  Rechtsschutzversicherungsgesellschaften eines
  Donaudampfschiffahrtsgesellschaftsmitarbeiters haben
  siebentausendzweihundertvierundachtzig Zeilen.}
  \bigskip
  \begin{itemize}
    \item \hy{Speicherverwaltungsadressen Rechtsschutzversicherungsgesellschaften}
  \end{itemize}
\end{frame}
\end{document}

Results with and without parbox:

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