Can I merge all my Google calendars into one?

No, you can't. You can't merge Google Calendars. As several others have described, you can easily have them all shown at once, visually merged, just by sharing the calendars with that single account you want to see them all in, but you can't inside an ordinary Google Calendar end up with just a single Calendar filled with content from several other calendars from separate accounts. However, what you could do is, use the Calendar API, with for example GAM, to pull all info from all your separate calendars into a single spreadsheet which you then sync to a single calendar. I'm guessing a Google Apps script would be easier than GAM, even though GAM is easy to schedule. Because as says below, the export/import is done at a single point in time, and needs to be done on a regular basis, to keep that single calendar up to date. Now, if the purpose of this is just to show other people what your calendar(s) look like, you can easily use the embed feature and show all your calendars on a single webpage, without actually sharing your calendar with anyone. Yes, that needs the calendars to be public, unless you know the viewers also have Google accounts. Then you can have all calendars published, but only those with the correct access rights will be able to see them all.

After a couple of hours looking for a solution for this (I needed an easy way for my co-workers to know my busy/free time, regardless of the calendar I scheduled my appointments (personal, projects, work, etc). I tried a couple of solutions and workarounds, and what really naiuled it for me is a service I found at http://scheduleshare.net. There you can: 1. Add one or more google accounts 2. Create a "Feed" for a combination of many of the calendars in those google accounts 3. Set what you're sharing, per calendar and per feed (details/ free-busy) Then you share the merged calendar link they provide with other people. They do charge a small fee, but it's the only viable alternative i have found so far. Note: I'm in no way affiliated with ScheduleShare.

Just share all the calenders with one account's email id and you would see the changes reflected in that account. This even allows other calenders to sync with each other. You don't need any external tool for this, its inbuilt in Google calenders. See this post for details http://harshtechtalk.com/merge-sync-different-google-calenders/

If by "merging" you mean "visually showing several calendars at the same time", than the answer is "yes", by adding them to "my calendars" or "other calendars", depending on the rights you have been given by the other calendar. If by merging you mean "consolidate several sets of events in to 1 calendar", than the answer is also "yes", by using the export and import functions within the Google calendar system. That obviously would be a 1 time action: the imported events could not be changed by the source calendar any more.