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Japanese Language Proficiency Test (JLPT)
serves as a proof of your language capabilities in Japanese
The test is made to be taken by non-Japanese people and it gives one a proof of your proficiency in Japanese. There are presently 4 levels in JLPT where level 4 is the lowest and 1 the highest. There's coming a new version of the test in 2010. This version will contain 5 levels instead of 4.

There is a rough estimation of the skills you're bound to have for each level, which can be seen in the table below.
Japanese Language Profficiency tabel The examination is split in 3 parts: "Kanji and vocabulary", "Listening comprehension" and "Reading comprehension and grammar".

For further reading about the test, take a look at these sites:
http://en.wikipedia.org/wiki/JLPT
The JLPT Study Page
the deblanck.org Mascot!