There are certain widespread assumptions in anarchist circles about philosophical anarchism: about what it is and what is wrong with it. My purpose in this chapter is to call these assumptions into question and to present a defence of what I describe as weak but engaged philosophical anarchism. Accordingly, I borrow my title (in slightly revised form) from one of the most influential works in the modest canon of philosophical anarchism: Robert Paul Wolff's In Defence of Anarchism (1976). This short essay has enjoyed significant academic attention (among political and legal philosophers), but is widely reviled in anarchist circles. While I oppose Wolff's strong but disengaged brand of philosophical anarchism, my reasons for this are somewhat untypical of his anarchist opponents, and we will examine their objections in due course, as well as my own.