<abstract><abbr title="too long; didn't read">too long; didn't read</abbr>: Back up with Time Machine before syncing your contacts via iCloud. If iCloud wipes out your contacts, you can restore the <c>~/Library/Application Support/AddressBook/</c> folder to get them back.</abstract> I regularly use two MacOS devices and one iOS device. Considering who else already has my contacts, I figure it was time, for convenience's sake, to use Apple's iCloud to sync my contacts across the three devices. I obviously not writing this article to inform the world that everything went smoothly. <ul> My desktop has the definitive list of contacts. My phone has a copy of these contacts, synced recently. My laptop has only a handful of contacts with only phone numbers.<fn> </ul> So how should I proceed? Well, obviously, turn on syncing contacts to iCloud from the desktop, to "prime" the contacts with the definitive list. Then, turn on syncing from the laptop and phone. I didn't expect any issues. What did I get? <ul> When I turned on syncing on the desktop, it didn't ask me anything. I didn't think anything of it. When I turned on syncing on the laptop, it asked if I wanted to <i>merge</i> my contacts to the cloud. I assumed that this meant it was going to merge with the contacts that had already synced from the desktop. I didn't expect any problems since the laptop contacts were duplicates of the existing contacts (names and phone numbers were already in the other list). At most, I figured I'd have to resolve an easy merge-conflict or two. The merge went seamlessly. However, I didn't see any of the desktop contacts show up on the laptop, even after waiting what I felt was an appropriate period. Instead, when I looked at the desktop, I was greeted with a very short list of contacts---the list of contacts from the laptop, in fact. <b>iCloud:</b> You keep using that word "merge"; I don't think it means what you think it means. iCloud leaned back and folded its hands, a job well-done. I had only the smallest possible list of contacts and all of my contacts I'd curated over two decades were gone. </ul> Well, I'm not an idiot, so they weren't <i>really</i> gone. But iCloud had made a bit of work for me. If this happens to you, you can get your contacts back by doing the following: <ol> Focus the <i>Finder</i>. Select the <c>Go</c> menu. Hold <kbd>(-opt)</kbd> to show the <c>Library</c> folder in the menu; select it to open a new <i>Finder</i> window. Browse to the <c>~/Library/Application Support/AddressBook/</c> folder Enter the Time Machine (I used the icon in the menu bar. Restore that folder to a previous version. You should see your prior contacts appear in the <i>Contacts</i> application. </ol> Syncing worked properly for me after that. It's still a mystery to me how this could have failed to work properly. Apple has enough engineers and syncing a few address-book items isn't rocket science. <hr> <ft>I'd done this on vacation, when I'd started using Messages more.</ft>