This is a common question and the answer may surprise you.
The answer is found in the Software License Agreement, also called the EULA. This agreement governs the use of your Adobe product.
How many systems can you install Adobe software on?
For individuals (as opposed to businesses) the software may be loaded on two computers, in most cases. The catch is that both computers must be used only by you and the two systems cannot be used at the same time. This policy was designed so that you could run (say) Creative Suite at home on your desktop PC, as well as while travelling with your laptop. But the types of computers and their usage has blurred so much now that you can just pick any two you own and the product should install and activate on both.
Here is an excerpt from the EULA for Photoshop CS6:
2.5 Portable or Home Computer Use. Subject to the important restrictions set forth in Section 2.6 [having to do with volume licensees], the primary user of the Computer on which the Software is installed … may install a second copy of the Software for his or her exclusive use on either a portable Computer or a Computer located at his or her home, provided that the Software on the portable or home Computer is not used at the same time as the Software on the primary Computer.
In other words, the primary user may install another copy on a secondary computer for their own use, but the two installations cannot be used simultaneously. Generally, for Creative Suite and Adobe Acrobat, the two machines should also be of the same operating system (Windows/Mac), because the software is licensed and delivered for use on a specific platform – but anyone who gets a “business license” can run the applications on both platforms. Subscribers to the Creative Cloud can also install the tools on both a Mac and a PC. Other Adobe products like Photoshop Elements and Lightroom are always sold multi-platform, making it a bit easier to mix-and-match Windows and Mac OS for your two installations.
Importantly, Adobe defines a computer as “a virtual or physical device,” not just a CPU – so that encompasses running on virtualization platforms such as VMware, Citrix, Parallels, and VirtualBox. The same thing goes for a dual-boot system with a product installed on both partitions, including Apple Boot Camp.
One additional requirement for upgrade versions of Adobe software: If you upgrade but want to continue using your prior release, then per Adobe licensing terms the older product must be on the same computer(s) as your newer upgrade version.
Note that these policies work exactly the same for Adobe’s Education versions – there is no distinction for those… However, one major difference in restrictions for the Student and Teacher Editions is they can be run only on the customer’s privately-owned computer(s).
So there’s your answer for most current Adobe software, although we recommend confirming the terms for your particular product or suite because the license agreements are somewhat different for each package (including Creative Suite, Acrobat, Lightroom, Elements, etc.) and version (CS3, CS4, CS5, CS5, CS6).
If you’re part of a company or business, and/or need more than one computer running the software at the same time, then you might want to take a look at the online discounts and ease of maintenance available through Adobe’s Volume Licensing Store. There you can save money, time, and headaches for multiple users.
Full EULA details are available here on the Adobe site.