Why can't I sync Photos on my Mac with Photos on my iPhone? I keep a subset of my photographs in Photos on my Mac, and I would like to sync these with Photos on my iPhone. I used to be able to do so, but the option seems to have gone away. The 'Sync Photos' checkmark in iTunes is now off, and if I turn it on, the only option is to sync the phone with a selected directory.



What's going on here? How can I enable Photos on the phone to sync with Photos on the Mac?
The solution, it turned out, was to quit Photos then relaunch it while holding down the Option key. It then asked me to pick a system photo library and I re-selected the existing system photo library. Then when I launched iTunes, "sync photos" gave me the option of syncing selected albums from Photos, as desired.

I've no clue what went wrong or why this would fix it, but it did.