How to merge iPhoto and Photo libraries on a Mac

Starting with OS X Yosemite 10.10.3, Photos replaced iPhotos on the Mac. If, like my wife, you kept using iPhotos before easing into Photos, you’ve probably got two different photo libraries on your Mac, which can be a pain and a storage hog. Thankfully, you can merge ‘em. To migrate another photo library manually: 

  • Quit Photos. 
  • Hold down the Option key and open Photos.
  • Select the library you want to open and then click Choose Library. If the library you want isn’t listed, click Other Library. Navigate to the library you want, and click Open.

And you should merge the libraries. Photos uses the same master files as iPhoto and the late, lamented Aperture, so you won’t need double the space to run both apps.

Don’t delete the iPhotos library until you’re sure that all your pics are in Photos. However, you can go ahead and free up hard disk space by moving the iPhoto library to an external drive and deleting it from your Mac. That way you’ll have a copy — just in case.