How many devices can I download my Itunes music to?

You can sync from your iTunes library to as many devices as you own. Automatic downloads are limited to a combination of up to 10 computers and/or devices.

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Manage your associated devices in iTunes - http://support.apple.com/en-us/HT204074 - In connection with, "When you turn on iTunes Match, Family Sharing, or Automatic Downloads, or when you download past purchases on your computer, iPhone, iPad, or iPod touch, that device becomes associated with your Apple ID. You can associate your Apple ID with up to 10 devices, with a maximum of 5 computers at any time. Each computer must also be authorized using the same Apple ID. You don't need to authorize your iPhone, iPad, or iPod touch. After you associate a device with your Apple ID, you can't associate that device with another Apple ID for 90 days."

[Old wording: "Your Apple ID can have up to 10 devices and computers (combined) associated with it. Each computer must also be authorized using the same Apple ID. Once a device or computer is associated with your Apple ID, you cannot associate that device or computer with another Apple ID for 90 days."]