CHCP.com

Change the active console Code Page. The default code page is determined by the Windows Locale.

Syntax
      CHCP code_page

Key
   code_page  A code page number (e.g. 437)  

This command is rarely required as most GUI programs and PowerShell now support Unicode. When working with characters outside the ASCII range of 0-127, the choice of code page will determine the set of characters displayed.

Programs that you start after you assign a new code page will use the new code page, however, programs (except Cmd.exe) that you started before assigning the new code page will use the original code page.

* The 65000/1 code pages are encoded as UTF-7/8 to allow to working with unicode data in 7-bit and 8-bit environments, however

Even if you use CHCP to run the Windows Console in a unicode code page, many applications will assume that the default still applies, e.g. Java requires the-Dfile option: java -Dfile.encoding=UTF-8

Unicode characters will only display if the current console font contains the characters. So use a TrueType font like Lucida Console instead of the CMD default Raster Font.

The CMD Shell (which runs inside the Windows Console)

CMD.exe only supports two character encodings Ascii and Unicode (CMD /A and CMD /U)

If you need full unicode support use PowerShell. There is still VERY limited support for unicode in the CMD shell, piping, redirection and most commands are still ANSI only. The only commands that work are DIR, FOR /F and TYPE, this allows reading and writing (UTF-16LE / BOM) files and filenames but not much else.

Defaults

The default code page in the USA is 437, the default in most of Europe is 850. The number of supported code pages was greatly increased in Windows 7. For a full list of code pages supported on your machine, run NLSINFO (Resource Kit Tools)

Files saved in Windows Notepad will be in ANSI format by default, but can also be saved as Unicode UTF-16LE or UTF -8 and for unicode files, will include a BOM.
A BOM will make a batch file not executable on Windows, so batch files must be saved as ANSI, not Unicode.

Examples:

View the current code page:
chcp

Change the code page to Unicode/65001:
chcp 65001

“Remember that there is no code faster than no code” ~ Taligent's Guide to Designing Programs

Related:

[Undocumented] CHCP - Forum.
Windows Locale codes.
TYPE - can print UTF-16LE files with a BOM regardless of the current codepage.
What every software developer must know about Unicode and Character Sets ~ Joel Spolsky.
Powershell: All text input is automatically converted to Unicode.
Equivalent bash command (Linux): LANG - locale category environment variable & LC_* variables for locale category.