Depends on what you mean by "Lisp". In the wider sense of the lisp family, there are obviously many differences (Clojure, Scheme, Common Lisp, etc.). If instead

Depends on what you mean by "Lisp". In the wider sense of the lisp family, there are obviously many differences (Clojure, Scheme, Common Lisp, etc.). If instead you mean Lisp == Common Lisp, the ANSI spec - which is a really well-made standard - is common to all implementations and basically works; for what came after that (threading, unicode, networking, etc.) the commercial implementations have their own extensions, while the open source ones rely on libraries, some of which are considered best practice.