What version of OS X is on your Mac?

It is easy to find out what version of OS X is on your Mac, just click on the Apple icon on the left end of the menu bar and choose About this Mac.

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About This Mac

If you then click on More Info… and scroll down to Contents and click on Software it will show more information:

Mac System Profiler

Here is the official line from Apple: OS X: Finding your OS version and build information.

The OS X version numbers and corresponding marketing names are:

• 10.0 Cheetah
• 10.1 Puma
• 10.2 Jaguar
• 10.3 Panther
• 10.4 Tiger
• 10.5 Leopard
• 10.6 Snow Leopard
• 10.7 Lion
• 10.8 Mountain Lion
• 10.9 Mavericks
• 10.10 Yosemite

There is more about these on: Wiki OS X.