Is God's name Yahweh or Jehovah? God's name is written as the Tetragrammaton יהוה‎ (YHWH) in the Old Testament. The name is not vocalized in the manuscripts and it's considered ineffable, forbidden to say aloud, by Jews. For that reason, the original pronunciation hasn't been preserved.

The two most commonly suggested possible originals are Yahweh and Jehovah. Long ago I heard it claimed that the vocalization Jehovah is based on a misunderstanding, but I don't remember the reasoning.

Which is the probable vocalization, or is it some altogether different one?
When a word isn't spoken, all you have to go by is its written representation.  Unfortunately, the written representation is incomplete, as ancient Hebrews only wrote consonants.  You were supposed to be able to infer the rest of the word from context, and you'd be familiar with them because you used most of them in day to day speech.

Oops!  Since the name of the Lord was not spoken aloud, the context needed for interpolation ended up being lost, and now we can only guess at it.  The theory is that "Jehovah" is the tetragrammaton with the vowels from adonai ("Lord", used in the place of the ineffable name) mixed in.  "Yahweh" is a guess based on trying to reverse-engineer the name into ancient Hebrew roots.  It may or may not be correct.