Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top.
Bmaj7b5 is B, D#, F and A# — Bmaj7 with the fifth lowered a semitone.
It sounds hollow and hard to place. Far more often met spelled the other way round, as a ♯11 over a chord that kept its fifth.

| B | D# | F | A# |
|---|---|---|---|
| 1 | 3 | ♭5 | 7 |
Coloured tonic — rare, and unstable for a major chord.
Also written BM7b5, BΔ7b5 or Bmaj7(b5). The same chord either way; which spelling you meet depends on who wrote the chart.
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
Bmaj7b5 has 5 of them, on strings 5-3-2-1, strings 6-4-3-2, the bottom four strings, the middle four strings and the top four strings, from open position up to the 8th — all in one inversion, so the bass note never moves. The one to learn first is the B shape at the nut.
Start with x2334x — no barre and down at the nut. None of the shapes for Bmaj7b5 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 3 of the 6 need a barre. Together they cover the neck from the 1st fret to the 11th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x21341 | 1st fret | B, root position | F | all fretted |
| x2334x | 2nd fret | B, root position | D# | all fretted |
| 768866 | 6th fret | B, root position | A# | barred |
| 78880x | 7th fret | B, root position | D# | barred |
| 7888x7 | 7th fret | B, root position | B | barred |
| x-x-9-10-11-11 | 9th fret | B, root position | D# | all fretted |
The same notes rebuilt from scratch give 14 drop 2 and 9 drop 3 voicings, each on its own page.
Tensions. A shell of Bmaj7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (C#) and the 13 (G#).
How you get to it. The turn that lands on Bmaj7b5 is C#m7 to F#7 — the ii and the V of B — and F#7 shares its third and seventh with C#m7, so the hand barely moves between them.
In which keys. Every note of Bmaj7b5 belongs to Eb minor (the ♭VI) and F# major (the IV, the subdominant).
Every note of Bmaj7b5 is in B lydian.
Change one note of Bmaj7b5 and you have Bmaj7 (the flat fifth becomes a fifth), Bmaj7#5 (the flat fifth becomes a sharp fifth), BmMaj7b5 (the major third becomes a minor third) or B7b5 (the major seventh becomes a flat seventh).
Bmaj7b5 is a major chord — root, major third, fifth. Major chords on every root.
On Bmaj7b5’s sound and use this page follows Robert Rawlins & Nor Eddine Bahha, Jazzology (Hal Leonard, 2005). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.