How do I import iphoto library to Photos?

When you do that, your iPhoto library will be upgraded for use with Photos. It would be wise to take a backup of it before importing, if you don't already have one.

Note also - that you will get a second library created containing just your iPhoto images - it won't transfer the images from the iPhoto library into your current library.

If you then want to merge the two libraries there are a number of ways you can do it.

Launch Photos with the Option key held down, click on Other Library, and choose the iPhoto one.

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