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.
C#maj9 is C#, E#, G#, B# and D# — C#maj7 with the ninth stacked above it.
It sounds a maj7 with more air in it. The ninth argues with nothing here, so it works anywhere a maj7 does.

| C# | E# | G# | B# | D# |
|---|---|---|---|---|
| 1 | 3 | 5 | 7 | 9 |
Tonic — an extended resting chord.
Also written C#M9, C#Δ9, C#ma9 or C# major 9. 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.
C#maj9 has 3 of them, on the middle four strings, the bottom four strings and the top four strings, from the 3rd fret up to the 10th — all in one inversion, so the bass note never moves. The one to learn first is the C# shape at the 3rd fret, which is the easiest grip here.
Start with x4354x — no barre and low, at the 3rd fret. None of the shapes for C#maj9 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 6 of the 11 need a barre. Together they cover the neck from the 1st fret to the 13th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x41111 | 1st fret | C#, root position | E# | barred |
| x4354x | 3rd fret | C#, root position | D# | all fretted |
| 44354x | 3rd fret | G#, 2nd inversion | D# | barred |
| x66668 | 6th fret | D#, 9th in the bass | B# | barred |
| xx6868 | 6th fret | G#, 2nd inversion | B# | all fretted |
| 966668 | 6th fret | C#, root position | B# | barred |
| 9-8-10-8-9-8 | 8th fret | C#, root position | B# | barred |
| 9-11-10-10-9-11 | 9th fret | C#, root position | D# | all fretted |
| x-x-10-10-9-11 | 9th fret | B#, 3rd inversion | D# | all fretted |
| x-x-11-10-13-11 | 10th fret | C#, root position | D# | all fretted |
| 13-11-11-13-13-11 | 11th fret | E#, 1st inversion | D# | barred |
The same notes rebuilt from scratch give 12 drop 2, 8 drop 3 and 13 rootless voicings, each on its own page.
Tensions. A shell of C#maj9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (F##) and the 13 (A#).
How you get to it. The turn that lands on C#maj9 is D#m7 to G#7 — the ii and the V of C# — and G#7 shares its third and seventh with D#m7, so the hand barely moves between them.
In which keys. Every note of C#maj9 belongs to C# major (the I, the tonic), F minor (the ♭VI), Ab major (the IV, the subdominant) and Bb minor (the ♭III).
Every note of C#maj9 is in C# major and C# lydian.
Change one note of C#maj9 and you have C#maj7 (drop the ninth), C#maj11 (add the fourth), C#maj13 (add the sixth), C#mMaj9 (the major third becomes a minor third), C#add9 (drop the major seventh) or C#69 (the major seventh becomes a sixth).
C#maj9 is a major chord — root, major third, fifth. Major chords on every root.
On C#maj9’s sound and use this page follows Mark Levine, The Jazz Theory Book (Sher Music, 1995). 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.