Microsoft Office 2013 can be installed on one PC, if you buy a new PC you'll have to buy a new license. Retail licenses start at $139.99 for the Home and Student version of Office 2013 and are bound to a single PC. In the software license agreement Microsoft states: "You may not transfer the software to another computer or user. You may transfer the software directly to a third party only as installed on the licensed computer, with the Certificate of Authenticity label and this agreement."
This means that once you've installed Office 2013 on a computer you can only use it on that computer and if you decide to buy a new computer you'll have to buy a new Office license. You are allowed to keep Office 2013 installed on a computer you sell, if you deliver the computer with a Certificate of Authenticity and the license agreement.
Previous retail Office versions, like Office 2010, allowed you to transfer it to another computer, as long as you installed the licensed software on a single device at once. The new agreement makes the retail Office 2013 version similar to the Office 2010 OEM licenses which could only be used on the computer it came with.
The license agreement also states that you're not allowed to lend the software and if you use the Home and Student version you're not allowed to use it for commercial, non-profit or revenue-generating activities.
It seems Microsoft is trying to make its retail versions less attractive to consumers. The company now also sells subscription based Office software, Office 365. The Office 365 Home Premium version comes at $99,- a year and allows you to install it on 5 devices.
