In the US, a simple explanation - as Peace indicated above says that once a composer has published a song (that is, made available for public sale more then 2000 copies) then anyone else can publish the song by securing a mechanical license (paying the per track fee of about 90 cents/track). Permission is NOT required. However; you are not free to change the song. I know in practice, minor changes are quite common - but material changes to another person's require written permission.