Rhythmic Contemporary, also known as Rhythmic Top 40, Rhythmic CHR or Rhythmic Crossover, is a primarily American music-radio format that includes a mix of EDM, upbeat rhythmic pop, hip hop and upbeat R&B hits. Rhythmic contemporary rarely uses rock or country in its airplay, but it may occasionally use a reggae, Latin, reggaeton, or a christian/gospel hit. Essentially, the format is a cross between mainstream radio and urban contemporary radio formats.
The origins of rhythmic top 40 can be traced back 1978 when WKTU on 92.3 FM in New York City (now WBMP) became a disco-based station. That station was classified as urban but played a blend of disco, dance music, and pop crossovers. At that time, stations playing strictly R&B tracks were known as black stations. Stations such as WKTU were known as urban. In the 1980s, many urban contemporary stations began to spring up. Most of these leaned towards R&B and away from a lot of dance music. These urban stations began sounding identical to so called black stations and by 1985, stations that played strictly R&B product were all known as urban stations. Still, some urban outlets continued adding artists from outside the format onto their playlist. In most cases it was dance and rhythmic pop but in other cases they added a few rock songs. But it wasn't until January 11, 1986 that KPWR in Los Angeles, a former struggling adult contemporary outlet, began to make its mark with this genre by adopting this approach. It would be known as crossover because of the musical mix and the avoidance of most rock at the time. Today, Mega 97ONE in Santa Maria broadcasts such a format. 
For years since its inception, the rhythmic name has been a source of confusion among music trades, especially in both Billboard (which used the Rhythmic Top 40 title) and Radio & Records (which use the CHR/rhythmic title for their official charts). In August 2006 Billboard dropped both the "top 40" and "CHR" name from the rhythmic title after its sister publication Billboard Radio Monitor merged with Radio & Records to become the "New" R&R as part of their realignment of format categories. The move also ended confusion among the radio stations who report to their panels, which was modified by the end of 2006 with the inclusion of non-monitored reporters that were holdovers from the "(Old) R&R" days.
Still, over the years since its inception, the genre has grown and evolved in its position between traditional R&B outlets (who claim that the Rhythmic contemporary format does not target or serve the African-American community properly) and the traditional Top 40 hit stations. However, both R&B and mainstream top 40 outlets have taken cues from the Rhythmic contemporary format through the years.