As the title asks. To what extent can you use actual brand names in writing without getting into legal trouble? Could you say that a character listens to his "ipod" or must you just say mp3 player? Are simple mentions of actual, real world brands ok? Likewise, could you have a character who is a major fan of a real world book or television or movie series or even a real world band make references to it/them and be described as wearing clothing items related to it/them? Or would such mentions of real world brands be problematic? In short, I want to know if real world brands can be used in a story and if so, where the line is between acceptable and not acceptable uses of them? If you have information on this I would be grateful if you could share.