An Introduction to Client Access License (CAL) is a license system widely used in the IT industry to regulate access to server software. CAL is a type of license that gives a user access permission to connect to a server and thus avail its various services. It is a type of license that comes with every Windows Server purchased. A CAL has to be purchased for every user or every device that requires access to the server. CALs come in various forms such as user CALs, device CALs. These licenses are essential in regulating access to server software such that organizations only use the software to an extent allowed by the license. CALs are usually purchased to enable end-users to be able to connect to a server and avail of its services. They are commonly used in organizations where employees use more than one device to access the server. The CAL system ensures that devices or users access the software according to the allowed limit, ensuring compliance with the license. CALs are especially useful in enterprises that find themselves in need of expanding their current infrastructure. When a company installs a new server or upgrades their current one, it has to purchase additional CALs to accommodate the new needs. The system is especially important in organizations seeking to stay compliant with licensing regulations, which if violated, can result in substantial penalties.