No, they're duck-typed. Types are attached to values, not variables, and for example trying to eval (+ 1 "hi") will throw a proper type exception. You usually

No, they're duck-typed. Types are attached to values, not variables, and for example trying to eval (+ 1 "hi") will throw a proper type exception. You usually don't have to declare types but for example in Common Lisp you can optionally declare types for better performance in speed-critical parts of the code.