Zermelo's approach to the well-ordering problem took place in three stages. He published a proof of WOT in 1904 (Zermelo 1904, an extract from a letter to Hilbert), where he first introduced the ‘choice’ principle, a principle designed (despite the name it has come to bear) to move away from the Cantorian ‘choosing’ arguments which almost universally preceded Zermelo's work, and which postulates that arbitrary ‘choices’ have already been made. This paper produced an outcry, to which Zermelo responded by producing a new proof  (1908a), which again uses the choice principle, but this time in a somewhat different form and expressed now explicitly as an axiom. The first three pages of this paper give the new proof; this was then followed by seventeen pages which reply in great detail to many of the objections raised against the first proof. These consisted in objections to the choice principle itself, and also objections to the unclarity of the underlying assumptions about, and operation with, sets used in the proof. This paper was followed just two months later by Zermelo's official axiomatisation (1908b), an axiomatisation which to a large degree was prefigured in the paper (1908a).