# JavaScript, 34ch #
    function f(n){return n?n*f(n-1):1}

<sub>*(or)*</sub>

    function f(n){return n?n*f(--n):1}

###Explanation

Function takes in a value, returns itself multiplied by  
**if n != 0:** the same function on the number decreased by one  
**if n == 0:** 1

The final f(0) returns first with 1, times 1, times 2, etc.

Terminator removed, may upset *use strict*.