http://en.wikipedia.org/wiki/I_am_that_I_am

I Am that I Am (Hebrew: pronounced Ehyeh asher ehyeh 
[ eh je aser eh je ]) is a common English translation (JPS among others) of the response God used in the Hebrew Bible when Moses asked for His name (Exodus 3:14). It is one of the most famous verses in the Torah. Hayah means "existed" or "was" in Hebrew; "ehyeh" is the first person singular imperfect form. Ehyeh asher ehyeh is generally interpreted to mean I am that I am, though it can also be translated as "I-shall-be that I-shall-be."^[1]

Ehyeh-Asher-Ehyeh, often contracted in English as "I AM" is one of the Seven Names of God accorded special care by medieval Jewish tradition.^[2] The phrase is also found in other world religious literature, used to describe the Supreme Being, generally referring back to its use in Exodus. The word Ehyeh is considered by many rabbinical scholars to be a first-person derivation of the Tetragrammaton, see for example Yahweh.