  We develop a novel approach to chiral meson-baryon dynamics incorporating
unitarity constraints and explicit resonance fields. It is based on the most
general structure of any pion-nucleon partial wave amplitude neglecting the
unphysical cuts as derived from the N/D method. This amplitude is then matched
to the one-loop heavy baryon chiral perturbation theory result at third order
and to tree level exchanges of baryon- and meson states in the s,t and u
channels. This generates the left-hand cuts. The unitarization procedure does
not involve form factors or regulator functions. The resonance parameters are
determined from fits to the S- and P-wave pion-nucleon partial wave amplitudes
for energies up to 1.3 GeV. In particular, the $\Delta (1232)$ is accurately
reproduced whereas scalar and vector meson couplings are less precisely pinned
down. We also obtain a satisfactory description of the $\pi$N threshold
parameters. Further extensions of this method to coupled channels and the
three-flavor case are briefly discussed.
