"Yahweh" is God's proper name. In Hebrew, the four consonants roughly equivalent to YHWH were considered too holy to pronounce, so the Hebrew word for "Lord" (Adonai) was substituted when reading it aloud. When vowel points were added to the Hebrew Old Testament, the vowel points for "Adonai" were mixed with the consonants for "Yahweh," which if you pronounced it literally as written, would be pronounced "Yehovah" or "Jehovah." When the Old Testament was translated to Greek, the tradition of substituting "Lord" for God's proper name continued in the translation of God's name to "Lord" (Kurios). Some English Bibles translate God's proper name to "LORD" or "GOD" (usually with small capital letters), based on that same tradition. This can get really confusing, since two other words ("Adonai" and "Elohim") translate to "Lord" and "God," and they are sometimes used together. The ASV of 1901 (and some other translations) render YHWH as "Jehovah." The most probable pronunciation of God's proper name is "Yahweh." In Hebrew, the name "Yahweh" is related to the active declaration "I AM." See Exodus 3:13-14. Since Hebrew has no tenses, the declaration "I AM" also implies "I WAS" and "I WILL BE." Compare Revelation 1:8.