A lead sheet or fake sheet is a form of musical notation that specifies the essential elements of a popular song: the melody, lyrics and harmony. The melody is written in modern Western music notation, the lyric is written as text below the staff and the harmony is specified with chord symbols above the staff.

The lead sheet does not describe the chord voicings, voice leading, bass line or other aspects of the accompaniment. These are specified later by an arranger or improvised by the performers, and are considered aspects of the arrangement or performance of a song, rather than a part of the song itself. "Lead" refers to a song's lead part, the most important melody line or voice.

A lead sheet may also specify an instrumental part or theme, if this is considered essential to the song's identity. For example, the opening guitar riff from Deep Purple's "Smoke on the Water" is a part of the song; any performance of the song should include the guitar riff, and any imitation of that guitar riff is an imitation of the song. Thus the riff belongs on the lead sheet.

A collected volume of lead sheets may be known as a fake book, due to the improvisational nature of its use: when presented with a lead sheet, proficient musicians may be able to "fake it" by performing the song adequately without a full score. This is in contrast to a full score, in which every note to be played in a piece is written out. Since fake books and lead sheets only give a rough outline of the melody and harmony, the performer or arranger is expected to improvise significantly.

A lead sheet is often the only form of written music used by a small jazz ensemble. One or more musicians will play the melody while the rest of the group improvises an appropriate accompaniment based on the chord progression given in the chord symbols, followed by an improvised solo also based on the chord progression. Similarly, a sufficiently skilled harmony player (e.g. a jazz pianist or a jazz guitarist) is able to accompany a singer or perform a song by themselves using only a lead sheet.

Lead sheets are not intended for novices. Sometimes, melodies with syncopation are written with the syncopation omitted, so the reader must be familiar with the songs "by ear" to play the melodies correctly.^{[example needed]} Some 32 bar forms do not have a printed melody during the "B" section, as the lead instrumentalist is expected to improvise one. Similarly, the chord progressions for some blues tunes omit the turnaround (often simply indicating two bars on the tonic), as it is expected that an experienced jazz player will know the appropriate turnarounds to insert (e.g., (I–VI⁷–ii–V⁷). The reader needs to have thorough familiarity with extended chords (e.g., C¹³) and altered chords (e.g., C^7♯11). Introductions and codas are often omitted, as it is expected that players will know the familiar intros and codas used on specific songs. Lead sheets are often bound together in a fake book.

Sheets containing only the chord progressions to the song are often called chord charts or chord sheets, to distinguish them from lead sheets. These sheets could be used by the rhythm section instruments to guide their improvised accompaniment and by lead instruments for their improvised solo sections, but since they do not contain the melody, they can be used in performances only by players who have the melodies memorized. Chord charts are commonly used at informal "jam sessions" and at jazz shows at small nightclubs and bars.

The melody, lyrics, and harmony define what a song is. In the music industry and entertainment law, a lead sheet is the document used to describe a song for legal purposes. For example, a lead sheet is the form of a song to which copyright is applied—if a songwriter sues someone for copyright violation, the court will compare lead sheets to determine how much of the song has been copied. If a song is considered for an Academy Award or a Grammy, the song is submitted for consideration in the form of a lead sheet.^{[citation needed]}