Interlisp-10, for Interactive Lisp, is an implementation of the Lisp programming language developed from 1966 at Bolt, Beranek and Newman (BBN) for TENEX, BBN's in-house PDP-10 operating system, and later DEC's TOPS-20 operating systems. From 1970, development of Interlisp was transferred to Xerox Palo Alto Research Center.

The language became popular with Stanford University AI researchers and at other principly US West-Coast institutions.

Interlisp was noted for its integration of interactive development tools into the the programming environment: debugger, Lisp-structure-aware editor, automatic correction tool, and analysis tools.

Start Interlisp with the EXEC command @INTERLISP:LISP. The Interlisp prompt character is a _. Return to EXEC with the Interlisp command LOGOUT() or Ctrl-C.

Note: Interlisp built-in function names should be typed in upper-case, although in many cases Interlisp can automatically correct names typed with incorrect case. Interlisp supports upper- and lower-case characters in user-defined names and in character string data.