Oldies is a term commonly used to describe a radio format that concentrates on a period 15 to 55 years before the present day.
In the early 2000s, 1970s music was increasingly included  , and 1980s music is beginning to also be called "oldies", though the term "classic hits" is used to distinguish the new oldies from the Baby Boomer oldies. 
Oldies tunes are typically from R&B, pop and rock music genres. Country, jazz, classical music, and other formats are generally not considered oldies music, although some of those genres have their own oldies format (for instance, classic country), and a number of songs "crossed over" from country to Top 40. Occasionally the term is used to describe the rare station that includes 1940s music as well, although music from before 1955 (coinciding with the "birth of rock'n'roll"), is typically the domain of the adult standards format. However, the term constitutes ambiguity for people who like old dancing music.
This format is sometimes called Golden Oldies (after another album series of the same name, which was sold through bulk TV commercials), though this term usually refers to music exclusively from the '50s and early '60s. Oldies radio typically features artists such as Elvis Presley, Chuck Berry, The Beatles, The Rolling Stones, The Beach Boys, The Supremes, The Four Seasons, and Sam Cooke; as well as such musical movements and genres as doo-wop, soul music, Motown, the British Invasion, early girl groups, surf music, and bubblegum pop.
Most traditional oldies stations limit their on-air playlists to no more than 300 songs, on the philosophy that average listeners will stay tuned provided they're familiar with the hits being played. The drawback to this concept is the endless repetition of the station's program library. Oldies has some overlap with the classic rock format, which concentrates on the rock music of the late-'60s and '70s and also plays newer material made in the same style.
Oldies stations as we know them today did not really come into existence until the early 1970s. In the 1970s, KOOL-FM in Phoenix, Arizona became one of the first radio stations to play oldies music, at that time focusing on the 1950s and early 1960s. KOOL is still playing oldies today. 
In the 1960s very few Top 40 Radio stations played anything older than a few years old. In the late 1960s a few FM stations adopted Top 40 formats that leaned towards adults who did not want to hear the same 30 songs over and over again but also did not want to hear easy listening music featured on MOR radio stations. They mixed in oldies with their current product and played new music only several times per hour. These radio stations were often referred to as "Golden" or "Solid Gold" stations. Some AM radio stations also began to employ this format. There were also syndicated music format packages such as Drake-Chenault's "Solid Gold" format, frequently used on FM stations that needed separate programming from their AM sisters due to the new FCC rules on simulcasting, that functioned as a hybrid of oldies and the adult contemporary and softer rock hits of the day. The popularity of the movie American Graffiti is often credited with helping to spur the 1950s nostalgia movement of the early 1970s, and it was out of this 1950s nostalgia movement that some of these stations, such as WHND/WHNE "Honey Radio" in Detroit, WCBS-FM in New York, WQSR Baltimore, and WROR in Boston, sprang up and were classified as Oldies stations and not Adult Top 40 stations. These stations, however, did play current product sparingly (one or two per hour) throughout the 1970s and into the 1980s; WCBS-FM, for example, played current hits under the moniker "Future Gold" as late as the late 1980s, and WLNG on nearby Long Island featured a roughly 50/50 mix of current hits and oldies from the early 1960s until about 1999. WGAR in Cleveland and KRLA 1110 in Los Angeles were other examples of Top 40 stations with heavy oldies orientations; KRLA was in fact promoted in the 1970s as the "Elvis-to-Elton" station.
Most of these "Solid Gold" stations began to either evolve into other formats or abruptly drop the format altogether from the late 1970s to early 1980s. Most AM solid Gold stations simply flipped to other formats. Some FM stations evolved into Adult Contemporary stations such as WROR Boston, WFYR Chicago, for example. Other FM stations simply moved into other formats like Rock, Top 40, Urban, or Country. In the early 1980s many Adult Contemporary stations began mixing in more oldies into regular rotation. Many of these stations had oldies shows on Saturday nights.
Gradually, beginning in 1982, both AM and FM stations began flipping to a full-time oldies format playing "All Oldies All The Time". These stations played strictly music from 1955 to 1973 focusing on the 1964 to 1969 era. By the mid to late 1980s stations like WDRC-FM Hartford, WODS Boston, WOGL Philadelphia, KLUV Dallas, WWSW Pittsburgh, WJMK Chicago, and many others sprang up. Some had as few as 300 songs while sations like WODS and WOGL had as many as 1500 songs in regular rotation. By 1989, most large and medium markets had at least one Oldies station. By 1990, most were on FM.
From 1986 to 1990 several solid gold stations evolved into full-time oldies stations by eliminating current and recent product, gradually eliminating 1980's songs, and even limited 1970's songs severely. KRTH and WQSR both did this in the late 1980s into the early 1990s. WCBS-FM, however continued playing current product in regular rotation until 1988. After that, they continued playing it once an hour between 11 p.m. and 5:30 a.m. until 2001. WCBS-FM also played several 1990's songs per shift during these over night hours. They continued also to play between one 1980's song every couple hours to as many as two per hour day and night. WCBS-FM also played between three and five songs per hour from the 1970s. They indeed played more 1970's music than any other notable oldies station. At the same time, WCBS-FM featured slightly more pre 1964 songs than the average station playing as many as five of those per hour.
Oldies stations continued to be late 1960s based throughout the 1990s. WCBS-FM was an exception. Most AM oldies stations also disappeared by the early 1990s except in markets where there was no FM oldies outlet. The format fared well with no end in sight.
In 2000, oldies stations began to notice their demographics were getting older and harder to sell. Still, at that time only a couple stations dumped the format altogether. A few went for a flavor of the months format called "Jammin' Oldies". But most continued to hang onto the format initially.
Since the turn of the century, stations began to limit selections from the '50s and early '60s. At the same time these stations began playing songs from as late as 1979 and even a few 1980s songs. WCBS-FM New York slightly cut back on the pre-1964 oldies and slightly increased the 1970s and 1980s songs early in 2001. They also eliminated the overnight currents and recurrents at the same time along with some specialty shows.
In 2002, many Oldies stations have dropped most music from before 1964 from their playlists, as it is believed that doo-wop and other music from the late '50s and early '60s appeals to demographics undesirable to advertisers, namely listeners over 65. As a result, many oldies stations have filled the holes in their playlists by extending their range through late-'70s. Some stations extended into the '80s. WCBS-FM canceled their Doo Wop Shop program and cut back to only one pre 1964 oldie an hour. By 2003, that station played under 50 such songs in regular rotation. Other stations eliminated pre 1964 oldies altogether with only a couple exceptions (Louie Louie, Shout, Johnny B. Goode for example).
From 2003 to 2006, most FM oldies stations such as KRTH, WOGL, KLUV, have evolved into classic hits (see below), classic rock, or gold-based adult contemporary formats (i.e. WHTT-FM in Buffalo, New York). Others simply dumped the format altogether.
The changes in selection have created some confusion over the definition of "Oldies", while many stations have adjusted their logos to accommodate their new formats. Stations that continue to use the term "oldies" in their on-air positioning generally do not play music made after 1979 (with some exceptions) and still may play one pre 1964 oldie an hour. Still, that is not always true. WODS in Boston still calls themselves "Oldies 103.3" but plays almost nothing from before 1964 (with the exception of their Sunday morning "Elvis Hour", during which they frequently play a number of Elvis' early recordings) and a moderate amount of early 1980s music. But most stations that do play post-1975 music have generally dropped the word "oldies" from their positioners, using identifiers such as "Super Hits," "Classic Top 40" or "The Greatest Top 40 Hits of All Time" (a la WRIT in Milwaukee and KLUV in Dallas/Fort Worth), or "Classic Gold" (a la the former format of CFCO in Chatham, Ontario, which has since switched to country music, or the now-defunct "Classic Gold" oldies-radio network in the United Kingdom). Many say "Greatest Hits of the 60s and 70s." WSRZ-FM in Sarasota, FL dropped their "Oldies 108" advertising nomenclature in favor of "Your Home Town Station" while expanding their playlist up to 1980. They still have their "Cruise In" segment for late '50'shttp://rocking50s.net and early '60's music. KQQL in Minneapolis/St. Paul and WLDE in Fort Wayne, Indiana, are two other examples of oldies stations which have relegated early and mid-1960s music to weekend specialty shows.
In 2003 Clear Channel's WSAI-AM launched the first "Real Oldies" branded station. It was created by Programmer Dan Allen and featured mostly the songs from the beginning of rock through the Summer of Love, 1967. It was a recreation of the WSAI that dominated Cincinnati ratings in the 1960's and early 70's and returned original WSAI DJs to the air, such as Dusty Rhodes, Jack Stahl, Ted McAllister and Casey Piotrowski. Unlike the 300 songs normally played, the Real Oldies format featured a very wide playlist and spawned clones all around the country. Soon, other radio stations such as WWKB in Buffalo, WCOL-AM in Columbus, and WRLL in Chicago adopted the "Real Oldies" moniker. Most of these "Real Oldies" stations were on the AM dial and featured legendary personalities from the '60s-'70s golden Top 40 era (for example, WLS legend Larry Lujack was part of the WRLL air staff).
Veteran New York radio programmer Scott Shannon developed a format known as the "True Oldies Channel," distributed via satellite by ABC Radio, which features some of the music featured on "Real Oldies" stations as well as hits of the late '60s and very early '70s, but generally nothing after 1975. The most high-profile "True Oldies Channel" affiliate is probably WLS-FM in Chicago, which adopted the "True Oldies" approach in the wake of WJMK's change to Jack FM. However, WLS-FM has slowly been adding more local personalities (including veteran radio personalities Greg Brown and Dick Biondi), and now only airs 'True Oldies' from 10am-3pm weekdays, overnights, and weekends. WIFO-FM Jesup, GA airs the True Oldies Channel during weekends as a contrast to its normal weekday country programming, and it is well received. True Oldies has also evolved to include more 1970's music and less pre-1964 product.
Many stations have since dropped the oldies format because of low ad revenue despite high ratings. On June 3, 2005, New York's WCBS-FM, an oldies-based station for over three decades, abruptly switched to the Jack FM format, resulting in a tremendous outcry from oldies fans in the Big Apple and a huge decline in revenue followed. WJMK in Chicago (WCBS-FM's sister station) switched to Jack FM on the same day. Some point to the demise of WCBS-FM and WJMK as a sign that the oldies format is in danger, for many of the same reasons that the adult standards and smooth jazz formats are disappearing. However, WJMK had been struggling for many years, and was in much worse shape than most other major-market oldies stations. In addition, unlike New York City (with the possible exception of WMTR (AM) in nearby New Jersey), the Chicago market has not technically been without an oldies station since, due to the existence of the aforementioned WRLL and now WLS-FM.http://www.keysdan.com/Oldies.htm
Yet another reason for the discontinuance of oldies stations in recent years is the attraction of a more lucrative format as an attempt to lure younger listeners. In 2001, Baltimore's WQSR (105.7 FM) and WXYV (102.7 FM) swapped frequencies, with WXYV being flipped from CHR/Top-40 to hip-hop at the same time, and WQSR retaining its oldies format. These two stations have since changed formats again, with 105.7 going to talk and eventually to sports radio, and 102.7 being a Jack FM station. In 2004, WWMG ("Magic 96.1") in Charlotte, North Carolina, switched to a Rhythmic CHR format and was renamed "96.1 The Beat". A new oldies station, nicknamed "Oldies 106.1" and carrying the WOLS callsign, now serves the Charlotte area.
The oldies format returned to WCBS-FM on July 12, 2007 in an updated form featuring music from 1964 to 1994 (and without the word "Oldies", but rather "Greatest Hits" in the on-air positioning), with songs such as "Girls Just Want to Have Fun" by Cyndi Lauper, "Gloria" by Laura Branigan, and "We Built This City" by Starship in rotation (though it should be pointed out that the original WCBS-FM played current hits mixed in with its oldies as late as the late 1980s and the three songs mentioned here during most of their years). Also included on the returning format as well are a sprinkling of pre-1995 hits and a selected number of classic oldies from the pre-1964 period. Thus far, the resurrected WCBS-FM has been well received. Still, WCBS-FM is positioned as "Classic Hits" rather than Oldies.
The oldies format remains one of the most popular formats on radio in markets where it is still active. Some of the most successful major-market oldies stations today really lean Classic Hits and include KRTH "K-Earth 101" in Los Angeles, XHPRS-FM "105.7 the Walrus" in Tijuana-San Diego, KOLA 99.9 in Riverside-San Bernardino, WODS "Oldies 103" in Boston, WOGL in Philadelphia, WMJI "Majic 105.7" in Cleveland, and KLUV in Dallas. WLS-FM in Chicago, however is similar to the way oldies stations sounded several years back. They still play one or two pre-1964 songs an hour during the day and as many as 4 an hour at night. However, to illustrate the continued decline in the format, San Francisco's KFRC moved toward Classic Hits in 2005 and dropped this format entirely in 2006 in favor of the Rhythmic AC "MOViN" format which left most of Northern California without an oldies station until the debut of KCCL (K-Hits 92.1) in Sacramento in January, 2007. (It should be pointed out, however, that KFRC had already evolved its format and positioning to classic hits at the time it changed to "Movin".) But KFRC was not gone for long. On May 17, 2007 with Free FM hot talk format failing on 106.9 KIFR CBS relaunched KFRC with a rock leaning classic hits format on 106.9. But KFRC was not back for long either. On October 27, 2008, 106.9 KFRC FM became an all news 740 KCBS AM simulcast. KFRC now only airs on 106.9 FM HD-2 and online at KFRC.com. But KFRC came back again. On January 1, 2009, KFRC returned on the radio at 1550 AM, as true oldies.
KZQZ (1430 AM), which airs in St. Louis, Missouri, has held onto the traditional oldies format. KZQZ, which began playing oldies in March of 2008, plays a wide variety of top 40 Billboard hits from the 1950s, 1960s, and the early 1970s.
WDJO (1160 AM), which airs in Cincinnati, Ohio, has also held onto the traditional oldies format. WDJO began playing oldies in February of 2006.
Jones Radio Networks, Waitt Radio Networks and Dial Global (formerly part of Westwood One) also offered 24-hour satellite-distributed oldies formats; the first two companies have been taken over by Dial Global's owner and the formats' futures are uncertain. ABC Radio actually offers two (three if Timeless is counted): in addition to the "True Oldies Channel," there is the much longer-running and more established "Oldies Radio" format (formerly known as "Pure Gold" during the time in the Satellite Music Network), which focuses mainly on the decade from 1965 to 1975 with some older and newer material.http://www.keysdan.com/Oldies.htm
In North America, Satellite Radio broadcasters XM and Sirius each have more than a dozen oldies radio channels, with XM offering separate stations for each decade from the '40s to the '90s, and Sirius doing the same for the '50s through the '80s. These companies also offer specific genre channels for disco and dance hits, classic rock, classic country, and vintage R&B and soul hits. http://www.xmradio.com/onxm/full-channel-listing.xmc,http://www.sirius.com/servlet/ContentServer?pagename=Sirius/CachedPage&c=ChannelLineup&cid=1139320914821These pay radio channels boast thousands of songs in their libraries, ensuring far less repetition than traditional broadcast stations. As of early 2007, the total number of satellite radio listeners is still under 15,000,000, but it's expected that this will increase over time. Music Choice similarly offers commercial-free music channels for most oldies or gold music genres similar to satellite radio.
See main article: Classic hits.
A variation on the classic rock theme is classic hits, which provides most of the playlist of classic rock with an addition of contemporaneous R&B and pop hits as well, striking a balance between the mostly '70s-focused classic rock genre and the more broad-based oldies format.