  We apply the effective field theory approach to the three-nucleon system. In
particular, we consider S=1/2 neutron-deuteron scattering and the triton. We
show that in this channel a unique nonperturbative renormalization takes place
which requires the introduction of a single three-body force at leading order.
With one fitted parameter we find a good description of low-energy data.
Invariance under the renormalization group explains some universal features of
the three-nucleon system ---such as the Thomas and Efimov effects and the
Phillips line--- and the origin of SU(4) symmetry in nuclei.
