Why do Jewish men sometimes wear a black box tied to their forehead?

This box is actually part of a two box set, called "Tefillim". The other small black box is tied to the right arm. The boxes contains biblical verses on parchment, and they use it for prayer which should be performed every morning, except on Saturdays ("the Jewish Sunday").

Note that only religeous (mostly orthodox) jews use this often. Most jewish friends I know only used this in their Bar Mitzvah (13th Birthday, which symbolizes the change from boy to man).

Also - some Reform Jewish Girls also use the Tefillim for prayer.

Hope this helps

These are phylacteries, or tefillin. There will also be one worn around the arm. This is a literal expression of Deuteronomy 6:8, stating that you should wear the word of god on your arm and on your head. The boxes contain the relevant texts.

They are called tefillin or phylacteries.

Religious articles worn during prayer:

http://www.google.com/search?hl=en&safe=off&defl=e...