  The Riordan group, along with its constituent elements, Riordan arrays, has
been a tool for combinatorial exploration since its inception in 1991. More
recently, this group has made an appearance in the area of mathematical
physics, where it can be used as a toy model in the theory of the
renormalization of scalar fields. In this context, its Hopf algebra nature is
of importance. In this note, we explain these notions. Power series play a
fundamental role in this discussion.
