MDL (Model Development Language, or colloquially also referred to as More Datatypes than Lisp or MIT Design Language) is a programming language, a descendant of the language Lisp. Its initial purpose was to provide high level language support for the Dynamic Modeling Group at Massachusetts Institute of Technology's (MIT) Project MAC. It was developed in 1971 on a PDP-10 running ITS and later ran on TENEX, TOPS-20, BSD, and AEGIS. In 1980 Marc Blank and Joel Berez adapted the MDL language to create a subset called which was used extensively by Infocom to create their award winning games.