iPhoto to Photos

Here is also an Apple Support document about the migration of Aperture Libraries. The same will work for iPhoto Libraries: Migrate your Aperture libraries to Photos or Adobe Lightroom Classic - Apple Support

In addition to Niel's advice: It will help not to jump in, but to get your iPhoto Libraries and Aperture Libraries shipshape before you migrate them to Photos. The reason is, that not all features of Aperture and iPhoto are supported in Photos. Do the tasks, that are better supported in iPhoto or Aperture while you can still use these applications.

• Notes on Migrating an Aperture Library to Photos for Mac, 2019 version
• Notes on Migrating an iPhoto Library from iPhoto to Photos for Mac

Drag each of them to the Photos icon in the Dock, or launch Photos with the Option key held down, click on Other Library, and choose them. You may want to import the iPhoto library into Aperture and then open only that one in Photos.

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