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We make the class of Moufang sets into a category in such a way that it is compatible with other categories (such as the category of quadratic Jordan division algebras). This note is not intended for publication as it is. 1 Another notation for Moufang sets We start by recalling the definition of a Moufang set. Definition 1.1. A Moufang set is a set X together with a collection of subgroups (Ux)x∈X, such that each Ux is a subgroup of Sym(X) fixing x and acting regularly (i.e. sharply transitively) on X \{x}, and such that each Ux permutes the set {Uy | y ∈ X} by conjugation. The group G: = 〈Ux | x ∈ X〉 is called the little projective group of the Moufang set; the groups Ux are called root groups. By the results of [1], every Moufang set can be obtained from a single group U (written additively, although not necessarily commutative) and