  We consider the 1D massless Dirac operator on the real line with compactly
supported potentials. We study resonances as the poles of scattering matrix or
equivalently as the zeros of modified Fredholm determinant. We obtain the
following properties of the resonances: 1) asymptotics of counting function, 2)
estimates on the resonances and the forbidden domain, 3) the trace formula in
terms of resonances.
