One chapter without numeration

How can I make one chapter (Introduction) without number?

I have:

\documentclass[12pt,a4paper]{mwrep}

\chapter{Introduction}
\chapter{Chapter 1}
\chapter{Chapter 2}


In ToC I have:

1. Introduction ..............1
2. Chapter 1 .................2
3. Chapter 2 .................3

I want to have:

Introduction .................1
1. Chapter 1 .................2
2. Chapter 2 .................3

I want introduction to behave just like the bibliography which is at the same level in ToC as chapters but without number.

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For the standard classes (article, report, book) you can use the starred version of \chapter which suppresses the number but also the TOC entry, so you hav to add it manually with \addcontentsline

\documentclass{report}

\begin{document}
\tableofcontents

\chapter*{Introduction}
\chapter{Chapter 1}
\chapter{Chapter 2}
\end{document}


or with KOMA-Script (scrartcl,scrreprt,scrbook) which provides \addchap for this case:

\documentclass{scrreprt}

\begin{document}
\tableofcontents

\chapter{Chapter 1}
\chapter{Chapter 2}
\end{document}


I don’t know about memoire’s behavior when using \chapter

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Why \addcontentsline{toc}{section}{Introduction}? In my document, it works without this line. –  Ichibann Jul 12 '11 at 22:06
@Ichibann: In this case you’re not using a standard class (article, report, book) in which the starred version suppresses the number but also the TOC entry. The \addcontentsline{toc}{<level>}{<text>} command writes the TOC entry. (See my edited post for KOMA-Script, which behaves in the same way for starred sectioning commands but provides the \addchap [and \addpart/\addsec] command[s]). See my edits … –  Tobi Jul 12 '11 at 22:10
MWCLS supports \chapter* and you don't have to do anything more, it will end in TOC, because Polish rules require it.