In the fields of physical security and information security, access control is the selective restriction of access to a place or other resource. The act of accessing may mean consuming, entering, or using. Permission to access a resource is called authorization.

Simply defined, the term “access control” describes any technique used to control passage into or out of any area. The standard lock that uses a brass key may be thought of as a simple form of an “access control system”.

Over the years, access control systems have become more and more sophisticated. Today, the term “access control system” most often refers to a computer-based, electronic card access control system. The electronic card access control system uses a special “access card”, rather than a brass key, to permit access into the secured area.