The box for Photoshop Elements for Mac OS has a note printed on it that says "Works with Apple iPhoto." This statement means that if you change the iPhoto preferences, you can open your images directly in Photoshop Elements when you double-click an image in iPhoto. You can also import an iPhoto catalog in the Elements Organizer.
Note: This statement does not mean that Adobe Technical Support provides any support for iPhoto. For support on iPhoto, contact Apple.
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Select the Elements Editor application file from the list of applications and click Open:
- Elements 9: Applications/Adobe Photoshop Elements 9/Adobe Photoshop Elements
- Elements 10: Applications/Adobe Photoshop Elements 10/Support Files/Adobe Photoshop Elements Editor
- Elements 11: Applications/Adobe Photoshop Elements 11/Support Files/Adobe Photoshop Elements Editor
- Note: Do not select the application file that has the same name as the parent folder, this file is the Welcome Screen launcher. For example, if you have version 9, then select the application file named "Adobe Photoshop Elements." DO NOT select the file named "Adobe Photoshop elements 9." See the following screenshot:

If not all the images you selected in iPhoto open in your chosen external image editor, open fewer or just one image at a time.
Disclaimer: Adobe does not support third-party software and provides this task as a courtesy only.
Note: Importing photos from iPhoto '11 in Elements 9 Organizer requires the 9.0.2 update. You can download this update here: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4918