A ledger line or leger line is used in Western musical notation to notate pitches above or below the lines and spaces of the regular musical staff. A line slightly longer than the note head is drawn parallel to the staff, above or below, spaced at the same distance as the lines within the staff (see Figure 1).

Although ledger lines are found occasionally in manuscripts of plainchant and early polyphony, it was only in the early 16th century in keyboard music that their use became at all extensive (Anon. 2001). Even then printers had an aversion to ledger lines which caused difficulties in setting type, wasting space on the page and causing a messy appearance. Vocal music employed a variety of different clefs to keep the range of the part on the staff as much as possible; in keyboard notation a common way of avoiding ledger lines was the use of "open score" on four staves with different clefs (Godwin 1974, 16–17).

Notes more than three or four ledger lines above or below the staff are usually considered hard to read.^{[citation needed]} When there are many notes in a passage requiring more than three ledger lines, it is often preferable to switch clef or use 8va notation. Some transposing instruments, such as the piccolo, double bass, guitar, and the tenor voice, transpose at the octave to avoid ledger lines.