iCloud Photo Library is Apple's answer to seamlessly syncing and storing your photos across all iOS devices, and in early 2015, with your Mac via the new Photos app as well. When enabled, iCloud Photo Library replaced the traditional Camera Roll and Photo Stream options with an All Photos section. It also removes the 30 days or 1,000 photos restriction. As long as you've got the iCloud storage to support it, iCloud Photo Library will store it.
Aside from syncing photos, iCloud Photo Library can also sync albums that you create on your iPhone or iPad. For example, if you create an album containing vacation photos on your iPhone, it will automatically be available on your iPad as well. The same goes for photos you favorite. iCloud Photo Library takes things a step further yet with non-destructive edits. If you make a change or edit a photo on your iPad, your changes will be applied across devices. If you ever change your mind about an edit you made, you can always revert back to the original photo, as iCloud Photo Library will store both versions.
Since iCloud Photo Library uses your iCloud storage allotment, you may find that you don't want to store full resolution photos on all your devices in order to save on storage space. iCloud Photo Library conveniently gives you the option to do so in Settings. Since this is on a device specific basis, you can enjoy full resolution photos on your iPad if you'd like, while only syncing storage optimized versions to your iPhone.
iCloud Photo Library is currently available in beta form on compatible iOS devices running iOS 8.1 or later. The new Photos app for Mac will also tie into iCloud Photo Library and is scheduled to be released in early 2015.
