This paper describes simple extensions to Common Lisp for concurrent computation on multiprocessors. Functions for process creation, communication, and synchronization are described. Multiple threads of control are created with process objects. Communication and synchronization are managed using mailboxes. Signals provide asynchronous communication between processes. SPUR Lisp includes future and delay values, which were first introduced in Multilisp. These features provide a flexible and efficient basis on which higher-level multiprocessing abstractions can be implemented and studied.