Macs that can be upgraded to OS X Mountain Lion or Later
1. iMac (Mid 2007 or newer) - Model Identifier 7,1 or later.
2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) - Model
Identifier 5,1 or later.
3. MacBook Pro (Mid/Late 2007 or newer) - Model Identifier 3,1 or later.
4. MacBook Air (Late 2008 or newer) - Model Identifier 2,1 or later.
5. Mac mini (Early 2009 or newer) - Model Identifier 3,1 or later.
6. Mac Pro (Early 2008 or newer) - Model Identifier 3,1 or later.
7. Xserve (Early 2009) - Model Identifier 3,1 or later.
To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right.
If your computer does not meet the requirements for the above, it may still meet the requirements to install Lion.
You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax. It's a download. You will get an email containing a redemption code that you then use to download Lion from the Mac App Store. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.
Lion System Requirements
1. Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7,
or Xeon processor
2. 2GB of memory
3. OS X v10.6.6 or later (v10.6.8 recommended)
4. 7GB of available space
5. Some features require an Apple ID; terms apply.
Are my applications compatible? See App Compatibility Table - RoaringApps.