  The S wave pion deuteron scattering length is presented at NLO in the
Effective Field Theory formulation of the two nucleon system with perturbative
pions. At this order, this observable is determined by the iso-scalar S wave
pion nucleon scattering length a^+, by pion re-scattering contributions inside
the deuteron and by two nucleon two pion contact interactions that involve two
unknown parameters which renormalise the appearing divergences. By choosing
their values accordingly and in agreement with their natural sizes predicted by
the power counting, we are able to accommodate the available experimental data.
However, a^+ cannot be determined from pion deuteron scattering directly. An
ongoing experiment at PSI aiming to reduce the error bars by an order of
magnitude will make it possible to pin down the size of these counter terms
more accurately. We compare our findings to an approach in which pions are
treated non-perturbatively.
