Launch Calendar, select File > Import > Import, and, in the window that appears, navigate to the file. Click the Import button, and an Add Events window appears. From its pop-up menu you can choose to add the calendar's events to any calendar already in Calendar's pane. Or, you can choose to create a new calendar. If you opt for the latter, the calendar will bear its original name. Alternatively, you can drag the calendar file to the Calendar icon in the Dock. Calendar will launch and display the Add Events window. Or drag a calendar into an existing calendar. Or just double-click on the file. All roads lead to import.
You can't incorporate calendar archive (.icbu) files into existing calendars. If you attempt to import one, you'll be told that you must replace (and lose) all of your current calendars with the calendars stored in the archive. Why on earth would you choose to do that? If you want an exact copy of your current calendars on another Mac (say a new MacBook Air you've purchased for travel) or within another account on your computer, you could simply import a backup file.
Sharing and publishing
It's hard to argue with the convenience of being able to send someone a copy of your calendar, but suppose you update that calendar. Do you really want to send updates each and every time you make a change to your calendar? Probably not. Thankfully, with the power of calendar sharing and publishing, you don't have to. Let's see what these two operations do and how they differ.
Sharing calendars with iCloud
If you've followed along with these lessons from the beginning (and if you haven't, you can start here), you should have an iCloud account by now. One of the many benefits of iCloud is that you can use it to share calendars. And it's not hard to do.
In Calendar choose File > New Calendar > iCloud. A new calendar will appear under the iCloud heading. Enter the events you'd like, and then choose Edit > Share Calendar. In the small window that appears, enter the email addresses of those you want to share the calendar with (separating each address with a comma). Click Done, and a link to your calendar will be sent to those you've chosen to share it with. Those sharing it will need an iCloud account to access your calendar.
By default when you share a calendar with someone in this way, they can edit the calendar--add and remove events. However, if you click on the triangle that appears next to their name in the Sharing window, you can choose View Only, which means they can see events added to the calendar but they can't create events of their own or delete existing events.
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