Beginning in early 90s, the theme music for most anime began to tend to be catchy songs deliberately written for release to the pop/rock music market, if they weren't already actual pop/rock songs, and by the new millennium, this trend was etched in stone, with an entire sub-industry in the music business, including an entire music label, dedicated to the creation of "anisong" tunes. As a result, in the new millennium in particular, the animation and music industries in Japan are tied extremely closely together, and artistic collaboration between the two is incredibly common.
The HistoryThis arrangement was not always the case, and the modern expression of it only came into full form in the lead up to and aftermath of the Turn of the Millennium. Japanese animation and cartoons have, by and large, always had music, of course; the modern "anime" industry came into being in the post-war era when sound had been part of motion pictures for three decades or more and Disney & Warner Bros. (both major inspirations for the early generations of Japanese animators) had been producing musical cartoons since the 1930s.
Much like the animation industry of the States, though, early Japanese animated series of the 60s and 70s tended to feature purpose-created theme songs, often in a rather big band style with either "smooth" (and arguably inoffensive) baritone singers or choirs of kids. (Mazinger Z and the early Astro Boy themes are nigh-canonical examples of the phenomenon in action.) Even as far forward as the original Mobile Suit Gundam, the theme was still being produced in this style (which became a bit memetic among the fan base, as the theme song was completely out of sync with the character of the rest of the show, especially the emotionally twisty back half).
It was Gundam and some of its contemporaries, however, that would start to transform things in the 1980s. While 1982's Super Dimension Fortress Macross had a commissioned theme song in the typical style, part of what made the show notable and attractive was the amount of original, not-obviously-Macross-branded music that the show produced, with a lot of it being quite catchy and memorable... and then the theatrical adaptation gave us the titular Do You Remember Love, which while critical to the narrative, was absolutely capable of being a stand-alone single.
Which it was. And which proceeded to almost completely vaporize the Japanese music charts of 1984, with the film's OST sitting at #9 and the DYRL single sitting at #7. For anyone to accomplish this would be impressive; for a song inspired by an animation to hang in the same chart as groups like The Checkers, twice over, was unheard of.
Contemporaneously, and perhaps inspired by this success, other shows began experimenting with different kinds of music for major themes, notably 1985's Zeta Gundam. The hotly-anticipated Gundam sequel opened with the jazzy "Zeta - Toki wo Koete" from Mami Ayukawa, which had still been written for the show, but aside from one reference to "believe in a sign of Zeta", there was no obvious indication it had anything to do with Zeta Gundam itself and could easily exist as its own song. This was due to its origins - it was essentially an adaptation of "Zeta" songwriter Neil Sedaka's own "Better Days Are Coming". He pulled a similar trick for Zeta Gundam's ending theme, with "Hoshizora no Believe" being adapted from "Bad And Beautiful".
Needless to say, the songs were again immediate smash hits, and the music and the show more or less helped to promote each other — fans of Gundam happily snapped up these new, highly fresh and memorable songs, while fans of Mami Ayukawa and Hiroko Moriguchi (who sang the second opening theme, "Mizu no Hoshi e Ai wo Komete", another Sedaka song "For Us to Decide"), not to mention Sedaka fans in the know, would check out Gundam out of curiosity.
The Sedaka connection, however, would end up being something of a licensing nightmare, particularly for potential releases of Zeta outside of Japan; since Sedaka was American, and the songs were adapted from his previous work, he still owned full rights and royalties for the songs in America, which made using them overseas, in America especially, prohibitively expensive since he and his music labels wanted the full rights to all related songs to be part of the package. They could still be used in the original context of the shows in Japan, but beyond that, their licensing was a nightmare (and years later even affected works like Super Robot Wars, who found it confoundingly difficult to consistently license "Zeta - Toki wo Koete" in particular).
This made the next step clear: cut out the "middleman" entirely and don't even bother with purposefully commissioning a song, and instead just license songs from an artist directly for use with a show, with a clear-cut contract from the start for the song's use in distribution.
It was 1986's Mobile Suit Gundam ZZ that would take this exact step; as was that show's wont, it flew off the expected rails from the very start by opening with "Anime ja nai", which was an 80s tech-rock piece from Masahito Arai that 1) was hugely unlike any previous Gundam opening (even Zeta having the jazzy Sedaka tunes which were somewhat in keeping with previous trends) and 2) had absolutely nothing to do whatsoever with the show. If anything, Gundam ZZ is possibly the single most "anime" Gundam show ever made by the hands of man, being Troperiffic in a way that original Gundam and Zeta never were; this gave the song an almost memetic power during the show's first run in Japan and became an emblem of how comparatively "weird" ZZ was compared to its stablemates. And thus, its single sold like crazy. When the show took a more serious turn later in its run, it switched to "Silent Voice" by Jun Hiroe, which was again a melodramatic rock piece with absolutely no link to the show, leagues away from the big band theme tunes of yesteryear. Fans loved it and helped it sell like hotcakes, too.
At this point, the writing was virtually on the wall; while the concept of commissioned themes for shows would continue to persist for a while longer, this emerging arrangement simply had too many advantages, for the artists and production companies both, for the wider industry to ignore, and the trend of licensing songs, or "encouraging" artists to come up with something on their own that could be used in a show, would begin to dominate and take the shape detailed below under "Why This Arrangement?". While commissioned theme songs in the style of the mid-century would still occasionally crop up, even in the 90s and the new century, in Kodomomuke shows and ones that focused on being Genre Throwbacksnote , by the time 1990 dawned, the "anime theme song" practice described by this entry had become the standard.
Why This Arrangement?One reason for all this, as the history noted, is simply that anime provides an easy way for both hit and entry J-pop/J-rock artists to get more exposure and good lateral promotion. Platinum J-rock bands like L'arc-en-Ciel and Orange Range frequently release their new songs along as themes in anime that are on the air at the same period as their respective singles or albums, and all kinds of careers (T.M.Revolution being one famous example via Rurouni Kenshin) have gotten a massive jump-start from being featured in a well-received show.
Another reason this is done is because many voice actors in Japan are also singers, often the more successful ones. (At least one such performer, Megumi Hayashibara, is both a formidable presence on Japanese pop charts and an internationally-known talent, as well as the recipient of more star and featured anime roles than any one person ought to have.) It's not unknown for production companies to organize some of their principal cast members into groups for recording CDs — the "Goddess Family Club" (Ah! My Goddess), DoCo (Ranma ½), the Maho-Dou (Ojamajo Doremi), Peach Hips (Sailor Moon) and the Spirit Singers (Digimon Frontier) all come to mind. Either way, it's usually to a voice actor's advantage — they perform theme songs (as well as additional "character" songs), receiving a double benefit from exposure in two different markets (and the additional profit).
A third reason is that, because of the developments detailed in the history above as well as parallel developments in live-action television occuring alongside it, TV theme songs are in some ways the pinnacle of Japanese musical success. If a Japanese artist/group makes a hit album, the studio takes almost all of the profits. If the same group makes an album as a TV tie-in, the musicians themselves receive a much larger cut.
As a result, many anime theme songs of the modern era, following those examples set in the mid-80s, have little to do with the subject matter of their shows. To western ears, it may just seem like they're singing about fate, destiny, and really nothing else in particular. Many are romantic songs of one flavor or another, ostensibly showing the point of view of one of the show's main characters. (This isn't limited to Shōjo or josei - there are plenty of cases of seemingly-"effeminate" love songs being used for Shōnen anime, once again probably encouraged by the precedent "Silent Voice" in Gundam ZZ, among others, set.) Alternately, they may be Thematic Theme Tunes, reflective "personality" pieces, nonsense patter songs, or instrumentals.
Whatever their style and content, though, anime theme songs are generally written and performed with the same attention and care that in the United States is reserved for potential Oscar-winning compositions. Quite a few can be very catchy - one example, "Hare Hare Yukai" from Haruhi Suzumiya, was been wildly popular as both a song and a dance at American and Japanese conventions for a decade or more.
InternationallyWhen an anime reaches the American and International broadcast market (as opposed to direct DVD sales), their theme songs are often either shortened or changed entirely. When a broadcaster does use new credits (Toonami and other outlets are notorious for not bothering to do so), a vocal performance may replaced with instrumentals; a case in point would be The Vision of Escaflowne, whose vocal song was traded for an "adventure-style music" opening. Other times the original melody is kept (perhaps with a little modification), and new English lyrics unrelated to the original are written for it; an example of this would be Sailor Moon, whose theme, "Moonlight Densetsu", was turned into a standard Western Expository Theme Tune Roll Call.
On the other hand, some importers have tried to create local language versions of theme songs faithful to the original Japanese lyrics, with mixed results. Difficulties have included license constraints on North American distributors from Japanese parent corporations, and the problem that American voice actors are rarely trained singers - as Viz's famously bad attempt to create "DoCo America" proved. In the late 1970s, Space Battleship Yamato's theme was dubbed reasonably well, even allowing for the changes that turned the series into Star Blazers, and the same was done in the 1980s with some of the themes from Ranma ½. Pioneer (later known as Geneon) sometimes did the same in following decades, even going so far as to release full English-language CDs for some of their imports. Funimation has revived the practice, with mixed results. Mexican and Chilean dubs of anime have also translated some songs, often with good results; the Latin Spanish versions of Mazinger Z, Science Ninja Team Gatchaman, Dragon Ball Z and You're Under Arrest! themes are as memorable and loved as the originals.
Very rarely, a replacement theme will prove to be more appropriate for English audiences (the Toonami run of Mobile Suit Gundam Wing's replacement of Just Love with an instrumental version of the show's original op being the most famous example). When this is successful, it's generally because the new theme stays more in step with English viewers' preconceptions of a series' tone.
The BizOne other thing of note concerning theme songs for anime: where in the United States a theme song is usually a vital part of the identity of a show (and, as noted up in the history, back in the 60s and 70s Japanese creators took a somewhat similar position), anime shows, especially in the new millenium, often change both opening and closing theme songs on a regular basis. The best example of this would be (again) Ranma ½, which had a different set of theme songs for each of its seven seasons and for its OVA series. Another good example is One Piece, which has (thus far) 18 openings and 18 endings in 692 episodes, or Detective Conan, which so far has a utterly staggering 39 openings and 49 endings. Similarly, episodes may feature several different renditions or versions of the same theme, as with "Fly Me to the Moon" from Neon Genesis Evangelion or "A-LY-YA!" from Negima!?.
The original lyrics to an anime theme song may be the occasion for Gratuitous English — the number of examples where English words and phrases are used instead of Japanese equivalents is vast. "Treat Or Goblins", the theme from Magical Shopping Arcade Abenobashi, contrasts Megumi Hayashibara's attempt at half-English hiphop with an all-English rap by an obviously American performer. In a few cases, the song is actually written mostly or entirely in English and performed at least in part by native English speakers — "Duvet", the theme from Serial Experiments Lain, and "Obsession" from .hack//SIGN are good examples. (One reason production companies may be doing this is to shortcut around the tendency, noted above, for American importers to ditch Japanese theme songs.)
The songs also frequently follow a specific pattern: the first verse is usually about a minute along (i.e., just the right size for a standard opening credit sequence), and changes to a different tune around halfway through. There is an instrumental of a few seconds before the song repeats, with different lyrics (although some will stay the same). The song then has a longer instrumental (throwing lyrics in there isn't unheard of, but they are always different to the lyrics from both verses), before repeating the second part of the first verse. Some anime like to play with this format: for instance, Neon Genesis Evangelion's theme, "The Cruel Angel's Thesis", had the longer instrumental (with lyrics for a few seconds) between the first and second verses, and had the rest of the song (second verse, lyrics in between, and repeat of half of first verse) in quick succession. This specific format is what's come to be known as the anisong, and many artists in the 21st century produce them independently with the hopes of having one or more picked up for use in a show. The record label Lantis, a company of its own before being folded back into the larger structure of its Bandai-Namco founder (though retained as a label itself), specializes in supporting artists who create songs for this purpose.
This doesn't just apply to just anime. Given the relationship between the game and animation industries in Japan (and how a lot of game creators have grown up on the examples cited elsewhere on this page), video games from Japan will also have theme songs in this style that are used in openings, endings, or cutscenes (with one example being "Suteki da Ne" for Final Fantasy X, and something like the opening to the first Growlanser being much more directly cut like the theme to an OVA of the period), and commercials to promote both singer(s) and game. Usually, the song will be released by the artists before the game itself is, and will have no actual ties to it, but occasionally the song will be written with the specific game in mind (a good example being Tales of Phantasia and "Yume wo Owaranai").
This page is example-less, as the trope is omnipresent, although especially noteworthy or career-launching examples are noted on the pages for various works. Potential sub-tropes are, naturally, a different story.
See also Image Song.