Music Publishing Companies make deals with songwriters and promote the songs their songwriters compose to musicians and anyone else who may need a song for whatever reason (advertising, a movie, a promotional campaign, etc.) They issue licenses for the use of the songs they represent and collect licensing fees.
They are different types of publishing companies. The Major Publishing Companies are Warner/Chappell Music, Universal Music Publishing Group, Sony/ATV Music Publishing. Then we have Independent Publishing Companies such as Kobalt Music Group and Imagem.
Music Publishers are companies that are interested in acquiring and exploiting the copyrights in compositions. They do not sign recording artist and they do not make records, shoot videos or commission remixes. They simply sign up writers (who may or may not be recording artists in their own right) and songs, collect money that’s generated by the use of their songs and occasionally help to place songs in adverts, movies and TV programs.
Talking about copyrights we have two of such - The copyright that exists in the recording and the copyright that exists in the composition. Publishing Companies are interested in the copyright that exists in the composition.
Where do publishers fit in the music industry then? Payments include using of songs embodied in records sold to the public, recordings used in commercials, recordings used in TV programs or movies, records that are broadcast and use of songs performed to the Public. Publishing Companies pay an advance to the writer as an incentive for the writer to assigne their copyrights to the publisher and the publisher will then control the compositions assigned for a period of time, normally 70 years.