If Photos is the spiritual successor to iPhoto, it’s only right that Photos can import your iPhoto library, and do so while keeping it intact—more or less ①. Because the features of Photos don’t align precisely with those in iPhoto, some information from iPhoto ends up in unexpected locations.

① An iPhoto library (left) migrates to Photos (right).
You’ll need to get used to the changes in Photos—and be prepared to change your approach to organizing your media—but Apple has worked to make the migration process as painless as possible.
The first time you launch Photos, it searches your system for iPhoto and Aperture libraries. If only one library fits the bill, it imports that library. Otherwise, it opens the Choose Library dialog (see Use Multiple Photos Libraries). Choose a library from the list, and Photos prepares the library for import.
In some cases, OS X may import your iPhoto library before you ever open Photos. Don’t worry—iPhoto will warn you if this has happened, and you can delete that unedited Photos library and re-import from iPhoto at any time without penalty.
When you import an iPhoto library into Photos, your existing library remains intact. The net result of the import is that you’ll have two separate libraries on your Mac’s drive: your old iPhoto library and a new Photos library ②. They’ll even have the same name—unless your library contained the word iPhoto, in which case you’ll see it replaced with the word Photos. (So a library called 2010 iPhoto Library will be imported to a library called 2010 Photos Library.)
② Your iPhoto library remains intact (left), but a new Photos library (right) comes into being.
If you have a large library, you’re probably worried that a second version of the same library will take up twice the space. But in fact, importing an iPhoto library into Photos uses almost no additional disk space. See the nearby sidebar, “Hard Facts about Hard Links,” for the nerdy details.
Apple has endeavored to transfer your data from iPhoto to Photos, even though several features (Events, star ratings) no longer exist. Here’s a guide to what gets imported, and what has changed during the transition.

④ Photos doesn’t have a concept of Events, so iPhoto Events are imported as albums.
Copyright © 2015, Jason Snell. All rights reserved.
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