I. Moerdijk: "On the Connes-Kreimer construction of Hopf algebras" Abstract: We give a universal construction of families of Hopf P-algebras for any Hopf operad P. As a special case, we recover the Connes-Kreimer Hopf algebra of rooted trees. Available from http://www.math.uu.nl/people/moerdijk/preprints.html. ---------------------------------------