Sometimes shortened to prog rock, a subgenre of rock music which arose in the mid-to-late 1960s, reached the peak of its popularity in the 1970s and has continued as a form of popular music to this day, enjoying a revival in the 1990s with bands such as Porcupine Tree and Deus Ex Machina. It is commonly associated with symphonic rock and art rock, although the term 'progressive' in today's usage often embraces a significantly wider spectrum of music than these styles.

The term was initially applied to the music of bands such as King Crimson, Genesis, Yes, Pink Floyd and Emerson, Lake and Palmer, who are widely regarded as prime exponents of the genre - but other examples of notable early progressive rock bands include Jethro Tull, Rush and Gentle Giant.

The characteristics of progressive rock can be difficult to define with precision - for example the above mentioned bands are different from one another in their respective sounds and fan bases. Progressive rock acts often combine rock formats with elements of classical music, or with styles such as jazz or jazz fusion. They also often reject specific genre norms and use uncommon musical structures and ideas. Progressive rock often uses a melodic or symphonic approach to songwriting.

Progressive rock songs typically avoid common song structures of verse, chorus, bridge, etc, or blur the formal distinctions by extending sections or inserting additional musical interludes, often with a wide dynamic contrast. Progressive rock often uses poetic, conceptually-themed or fantasy-based lyrics. Rhythms often include time signatures and techniques uncommon in rock music and are often unsuitable as dance music.

Instrumentation frequently includes keyboards or synthesizers in addition to the usual rock range, and often other instruments common to classical and jazz genres, such as saxophone, flute and violin. Some progressive acts have incorporated orchestras and choirs. The Mellotron in particular was generally a signature sound in many progressive acts such as the Moody Blues, King Crimson and Genesis, with later bands such as Emerson, Lake and Palmer and Yes making extensive use of synthesizers. The German group Kraftwerk incorporated a wide range of electronic sounds, including one of the first uses of electronic percussion.

The styles and often lengths of the pieces mean that this music is album-oriented rather than singles-oriented. Progressive rock bands often use concept albums (aka 'rock operas'), in which a theme or storyline is explored throughout an entire album or series of albums, sometimes in a manner similar to a film or a play. A notable example is Pink Floyd's The Wall, which was followed by a film of the same name and an elaborate live show).

Some progressive rock bands became as well-known for the art direction of their albums as for their sound, using visual elements to aesthetically link with the music and create a strong overall musical identity. This led to fame for particular artists and design studios, most notably Roger Dean for his work with Yes and Storm Thorgerson and his studio Hipgnosis for their work with Pink Floyd. H.R. Giger painted an album cover for Emerson, Lake and Palmer's Brain Salad Surgery.

In recent years, one of the more commercially viable categories of prog has been progressive metal, which mixes some of the common elements associated with progressive rock (lengthy compositions, concept albums, odd time signatures, virtuosity, jazz fusion influences) with the power and attitude associated with metal.