  We discuss the contributions of lepton-number-violating sources to
neutrinoless double beta decay ($0\nu\beta\beta$). Assuming that these sources
arise at scales well above the electroweak scale, they can be described within
an effective field theory. Here, we outline the steps required to express the
$0\nu\beta\beta$ half-life in terms of the effective interactions, focusing on
the dimension-five operator that induces a Majorana mass for the neutrinos.
This process involves the evolution of the operators down to scales of a few
GeV where they can be matched onto Chiral Perturbation Theory. The resulting
Chiral Lagrangian can then used be to derive the lepton-number violating
potential, which, in combination with many-body methods, gives the
$0\nu\beta\beta$ half-life. We will show that consistent renormalization
requires the inclusion of a new contact interaction at leading order in this
potential. We also briefly comment on the constraints that can be set on the
operators appearing beyond dimension five.
