Lisp 1.5 is an ancient dialect from around 1962. The first implementation appeared on IBM mainframes (IBM 704, 709, 7090, 7094), but other implementations appeared on other systems. Some source code survives on the internet, but it seems that no one can run Lisp 1.5 programs today.

Lisp 1.5 is an implementation of Lisp. Other implementations of Lisp.

The features of Lisp 1.5 include garbage collection (of cons cells), recursion, and runtime evaluation (by an eval function).