Book excerpt: Your Apple ID is much more than a simple username. It's a key that unlocks a long list of Apple products and services on any of numerous devices. iCloud uses an Apple ID, as does Apple Music; the App Store; the Music, TV, and Books apps; and more. An Apple ID protects your personal information, including email and iOS/iPadOS backups; helps you find a lost iPhone; and can even unlock your Mac. So it goes without saying that if something goes wrong with your Apple ID, you could be in for a world of hurt. Unfortunately, things go wrong with Apple IDs all the time. Fortunately, Glenn Fleishman, a veteran technology journalist and the author of Macworld's "Mac 911" column, is ready to help with expert advice on how to manage your Apple ID-including how to prevent, solve, or work around most common problems! In this book, Glenn answers questions like: What all is my Apple ID used for? How does my iCloud account relate to my Apple ID? What problems can two-factor authentication (2FA) solve, and how do I use it? Are there other mechanisms I can use to ensure that I can recover an Apple ID in the event of a problem? (Spoiler: yes!) What if I have a device that's too old to work with two-factor authentication? What should I do if I have two or more Apple IDs or iCloud accounts? Will I lose access to all my Apple media purchases if I move to another country? Can I share an Apple ID with someone else? What exactly should I do if I think someone is hacking my Apple ID account? How can I recover a forgotten Apple ID password? What steps should I take if Apple locks me out of my account? If I lose access to an email address associated with my Apple ID, what can I do? What Apple ID changes in iOS 13/iPadOS 13 and macOS 10.15 Catalina do I need to know about? And that's just the beginning. Glenn has packed a remarkable amount of concise problem-solving information into this compact, 90-page book. Read it before you encounter Apple ID problems to minimize your risk, and if you've already encountered a problem, read it to find the best path to a rapid solution.