....copying is not always infringing. If the work is not copyrighted, if you have a license to make the copy, or if the work is in the public domain, you can copy at will. Also, not all "copies" are the same. Say you buy a CD and play it on your computer — technically, you have already made a "copy" onto the PC in the process of playing it, but that's not an infringement.

Making an archive copy is okay too, as long as your retain the original. What about a transformative copy — say, making an MP3 out of a CD? You can do that, so long as you retain the original work. If the original CD get scratched, damaged or lost, you can probably burn the MP3 back to a CD (sans the really "sucky" titles), but this is not entirely clear.

.... if you make copies for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, it is not an infringement of the copyright, even if the copyright holder does not want you to do so.

This isn't black and white, of course. In deciding whether a use is fair or not, courts will consider a number of factors: Did you make the copies for commercial purposes? Does the copy deprive the copyright holder of revenues? Did you copy all, or substantially all, of the work, or just a small portion? The less of the work copied, the less commercial and the less impact on the copyrighted work, the more likely it is to be considered "fair."

....The problem for the RIAA and MPAA is that all they can see is that someone is copying a work — they cannot tell the purposes for which the work is being copied. Therefore, when they sign an affidavit to get a subpoena alleging a copyright "infringement," all they really know is that a copy has been made, not that an infringement has occurred.

....The law imposes four kinds of liability for infringement. The simplest is direct infringement — meaning you or somebody under your direct control (your agent) actually infringes. A second type of infringement is contributory infringement or vicarious infringement — you aid someone else's infringing activities, or you profit from their infringement and have the ability to control them. It is this theory that makes owners of P2P networks potentially liable.

A third category of infringement is implicated if you provide the technology to aid the infringement (e.g., the Sony Betamax case.) In that case, you are liable for the infringement others do with your technology, unless there is a "substantial non-infringing use" for your technology (e.g., time shifting TV shows.) Finally and most recently, the DMCA creates a new "circumvention" liability" — creating or disseminating technologies that are designed to circumvent a technological measure protecting a copyrighted work.