What causes iTunes and/or the App Store to disappear on my iPhone?

I've never tried to delete either iTunes or my App Store. What causes this and how can I get them back?

First make sure that it isn't hiding in an app drawer (folder). If you don't have luck there, go to Settings and make sure that iTunes and the App Store are both turned on. Then go to Settings > General > Restrictions. It may be passcode protected, or even prompt you to set a passcode. Check there to make sure that iTunes and the App Store are not blocked.

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