Copyright law deals with protecting creative expression fixed in a tangible medium. Copyright arguably covers just about everything we write down or record. Since 1989, when the formality of the copyright notice was made unnecessary, everything with a minimal amount of creativity in it that has been written down, saved to a hard drive, recorded to tape, or otherwise fixed is protected by copyright. That means that you may have valuable assets in the form of written expression that you could be commercially exploiting. It also means that you have to be careful not to infringe on the rights of others.