This is a question that has been answered many times over the years. Search for "why common lisp" and you'll get a long list of them. The answers now, IMO, are

This is a question that has been answered many times over the years. Search for "why common lisp" and you'll get a long list of them. The answers now, IMO, are not substantially different than they were, say, ten years ago. The big differences, I think, are the new competitors in the LISP world: the rise of Clojure, and the rebranding and further development of PLT Scheme as Racket.