It's almost impossible to put your finger on something as amorphous as ambient music. In spite of mounds of academic writing and manifestos on the subject, the genre remains as elusive and gauzy as ever.

One common idea is that ambient is a description of space, or an attempt to use the shape of the sound as the foreground subject (instead of vocals, melody or classic/pop song structure). Perhaps a concise definition could be: music for liminal spaces, either real or imagined.

In 2015, ambient is most often found in private settings or art-related spaces: museums, galleries, college concert halls. But once upon a time in the '90s, chill-out rooms playing ambient music at raves and electronic music festivals were common. By the late '90s, that scene had receded into the background, but the 21st century has seen the rise of many new voices in ambient: Fennesz, Oneohtrix Point Never, Colleen, Emeralds, Rashad Becker, Holly Herndon, Grouper, Dalhous, Bing & Ruth, Nils Frahm, and many more.

The following list is ambient for beginners. We kept it to proper albums and limited it to the 20th century. And we included a high concentration of “concept albums,” which is a popular format for ambient producers. By pinning themselves to something specific and of this world, the composers allow themselves the freedom to explore abstract forms and sublime cosmic architecture.

10. Wendy Carlos, Sonic Seasonings (1972)

This early work by synth pioneer Wendy Carlos (which, unfortunately, is not available online) was released a year after she composed the score for A Clockwork Orange. Many ambient producers have had success scoring films, as the nature of ambient music and the dreamlike language of cinema go together like crystals and patchouli. As the years go on, Carlos' influence as one of electronic music's most enduring tinkerers has become more and more apparent. Seasonings is a gorgeous piece divided into a sections devoted to each of the seasons, as if Vivaldi was into modular synths.

9. Tangerine Dream, Phaedra (1974)

Not all ambient music is fluffy clouds. For their fourth studio album, this prolific German group (who also went on to compose for films) created their seminal work, Phaedra, which captures them in the net of some galactic drama that verges on opera. This was the first time they used the Moog sequencer (and one of the first commercial records to feature sequencers of any sort), so their process had to be rewired. In fact, their inexperience with the gear led to accidental happenings, such as the recording of the title track. The album was released to wide acclaim, thanks in no small part to an endorsement by John Peel, which helped land the album on U.K. charts.

8. Cluster and Brian Eno, Cluster & Eno (1977)

Brian Eno left the influential art-rock group Roxy Music in 1973, citing boredom and disinterest with the rock & roll lifestyle. The restless experimentation and exciting collaborations he sought would soon come in many forms, one of the highlights of which is his first album with krautrock/kosmische heroes Cluster, aka Hans Joachim Roedelius and the recently deceased Dieter Moebius. While their second LP of co-written material opted for more pop arrangements, it's their first joint effort, Cluster & Eno, that feels as contemporary as anything on this list.

7. Brian Eno, Ambient 1: Music for Airports (1978)

Brian Eno didn't invent the ambient genre, though a lot of people assume he did. But he did bring it much wider attention, and his definition of ambient is still the definition many people use. In his liner notes for this landmark album, he writes, “An ambience is defined as an atmosphere, or a surrounding influence: a tint. My intention is to produce original pieces ostensibly (but not exclusively) for particular times and situations with a view to building up a small but versatile catalogue of environmental music suited to a wide variety of moods and atmospheres.” It turns out that a lot of ambient music is about space, flight and suspension. This is the album that connects the dots of being between two places, with the familiar liminal space of much ambient music represented by the airport. Music for Airports would be the first in his influential Ambient series.

6. The KLF, Chill Out (1990)

British acid house pioneers The KLF are perhaps most famous for burning a million pounds. But their rebellious, Illuminati-obsessed, art-school attitude belies the subtle beauty of their work. Chill Out is their undisputed masterpiece, following a long tradition of the English looking to the American South for inspiration. A concept album, Chill Out conjures a late night train ride from Texas to Louisiana in some imaginary theater of the mind. With field recordings and sounds cribbed from BBC documentaries and sound effects albums, Chill Out incorporates seemingly disparate parts — country, trance, preacher sermons, dub, and classical — into an effortless, ghostly rave that's somehow always been there. While they're not as famous as they should be here in the States, The KLF bridged the gap between house and ambient, esoteric and approachable, abstract and narrative, and this recording ushered in a new era of interest in the ambient genre.

5. Aphex Twin, Selected Ambient Works 85-92 (1992)

If you only ever hear one album by living rumor machine Richard D. James, this is the one. “Xtal” is the perfect opener, a warm invitation to a womb-like subterranean world ruled by benevolent dolphin gods. And unlike most of the LPs on this list, Selected Ambient Works feels more like individual tracks or songs that work just as well as on their own as they do as part of a whole.

4. The Orb, The Orb's Adventures Beyond the Ultraworld (1991)

The Orb looked at what The KLF did and took it one step further. The Orb (aka the KLF-affiliated Alex Paterson and a rotating cast of collaborators) were not shy when it came to sampling. Their recipe was full of found sound, speeches and field recordings, dubbed and mixed on top of original instrumentation — which was pretty novel at the time. This would vault The Orb into star status, and Paterson, along with co-producer Thomas Fehlmann, is still at it today.

3. Global Communication, 76:14 (1994)

This first full-length from Tom Middleton and Mark Pritchard's Global Communication project is a prime example of British ambient electronic music in the mid-'90s. Perhaps in a nod to minimalist composer and ambient forefather John Cage, who once “composed” a piece called 4'33″ that was four minutes and 33 seconds of silence, all of the tracks on 76:14 are named simply after their length. “14:31” is the standout, the sound of star systems leisurely running through their life cycles, with a curious melody that sticks in your head for weeks and years after hearing it. Unlike some of the British peers, Middleton and Pritchard eschewed sampling in favor of generating original sounds. If there is intelligent life out there, these are the peaceful melodies we should be broadcasting to them.

2. Tetsu Inoue, Ambiant Otaku (1994)

Japanese producer Tetsu Inoue's Ambiant Otaku was mythic for most of the '90s, as it was released in a very limited run, and torrenting wasn't a thing yet. People seeking out his minimalist, John Cage-esque take on the genre were ready to hand over princely sums for this record. Since then, this seminal work has been re-issued and showcases a restrained sense of beauty.

1. Gas – Königsforst (1999)

Gas is one of over 30 aliases German wizard Wolfgang Voigt releases music under, but it's probably his most well-known. This third Gas full-length features the most uptempo, 4/4-kick-led compositions on this list, and many of these songs could fit neatly in the club, as they all clock in somewhere around 120 beats per minute. Named for the forest near his hometown of Cologne, where he dabbled with psychedelics, Königsforst skirts the line between pulsing nocturnal dreamscape and hypnagogic nightmare that, as Voigt put it, “has no ending and no start,” much like the musical continuum Gas is a part of.

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