This paper contains some basic results on 2-groupoids, with special emphasis
on computing derived mapping 2-groupoids between 2-groupoids and proving their
invariance under strictification. Some of the results proven here are
presumably folklore (but do not appear in the literature to the author’s
knowledge) and some of the results seem to be new. The main technical tool used
throughout the paper is the Quillen model structure on the category of
2-groupoids introduced by Moerdijk and Svensson.

We give an explicit handy (and cocycle-free) description of the groupoid of
weak maps between two crossed-modules using what we call a {\em papillon};
Theorem 8.3. We define composition of papillons and this way find a bicategory
that is naturally biequivalent to the 2-category of pointed homotopy 2-types.
This has applications in the the study of 2-group actions (say, on stacks).