A track from Madonna's debut album, this was written by her producer Reggie Lucas, who also wrote her song "Physical Attraction" (Madonna wrote or co-wrote all the other tracks except "Holiday"). The song is a great example of a writer tailoring a song for a specific artist - few would guess that this was written by a man.
Lucas got a sense for what Madonna was all about by listening to her demo tapes and watching her perform. He then wrote "Borderline" specifically for her, playing up her sensual side. Lucas hasn't discussed the specific inspiration for the song, but many fans speculated that the lyrics are about having an orgasm. At this point, Madonna was still quite subtle about her sexuality, but as her career matured, she made sex an open topic, releasing overtly sexual songs like "Erotica" and "Justify My Love," and even releasing a book on the subject, simply titled Sex
As for Reggie Lucas, he also wrote the Roberta Flack & Donny Hathaway hit "The Closer I Get To You
" (#2, 1978), and the Stephanie Mills song "Never Knew Love Like This Before" (#6, 1980).