Selling client-access licenses (CALs) is big business for Microsoft. In fact, it's believed to be a $1 billion a year business for the Redmondians.
CAL licensing is a regular source of confusion, and something about which I and no doubt other Microsoft watchers get lots of questions.
Any user or device that accesses Microsoft server software directly or indirectly legally requires at least one CAL, Microsoft officials say. There are a number of different types of CALs: Device CALs, User CALs, Base and Additive CALs, Premium CALs, Enterprise CALs and more. Different Microsoft products often require different kinds of CALs. And "external users" -- those who aren't employees or onsite contractors -- also may require CAL coverage, too.
On March 10, the Microsoft Licensing team attempted to make CAL licensing a bit less murky by posting seven CAL questions and answers to Microsoft's Volume Licensing blog. Among the topics addressed are everything from "Does my multifunction printer need a CAL?" (short answer, yes, if connected to a Windows Server network), to "Can I use my CALs to access someone else’s server?" (yes, if they are "affiliates").
The volume licensing team also posted links to a few additional CAL-related resources, including "Base and Additive CALs: An explanation" and "About Licensing -- Client Access Licenses and Management Licenses."
I've taken an occasional stab at trying to parse the Microsoft CAL licensing terms in areas such as CALs required for Remote Desktop Services on ARM-based Surfaces. Definitely headache-making stuff. So anything like the latest Q&A is most welcome.
Update: As a few readers noted, if you have to ask whether you are supposed to pay for a CAL, the Microsoft answer is far more often than not, "yes." But there are still questions worth asking to make sure you don't overpay for CALs.