  We discuss an on-shell approach to pion-nucleon physics that is consistent
order by order in a $1/f_{\pi}$ expansion with the chiral reduction formula,
crossing, and relativistic unitarity. A number of constraints between the
on-shell low-energy parameters are derived at tree level in the presence of the
pion-nucleon sigma term, and found to be in fair agreement with experiment. We
analyze the nucleon form factors, and the $\pi N\to \pi N$ scattering amplitude
to one-loop, as well as $\pi N\to\pi\pi N$ to tree level. We use the latter to
derive a new constraint for the pion-nucleon sigma term at threshold. We
compare our results to both relativistic and non-relativistic chiral
perturbation theory, and discuss the convergence character of the expansion in
light of experiment.
