The MP3 format itself is not illegal. MP3 is simply an audio compression file format, analogous to the ZIP file compression format popular with PC users, or the JPEG graphic file format used in software like PhotoShop or Illustrator. By law, you are permitted to make a personal copy of your music (i.e.- making a cassette copy of a CD), this includes converting CD files into MP3 formatted files.
Due to its quality and relatively small file size, MP3 formatted music has been increasing distributed online, with and without permission from copyright owners.
Although these emerging technologies and music networks enable users to share music freely and easily online, as it stands now, it is illegal to distribute copyrighted music online, unless it is under digital rights management.
Many, however, use this new audio technology for completely legitimate purposes. MP3, being an open standard, has quickly gained wide acceptance on the Internet. It is now the de facto format for digital music file compression and digital audio on the web.
More people listen to MP3 music, use MP3 software programs and hardware devices than any other compressed CD-quality audio format today.