  We analyze the CP-violating electric dipole form factor of the nucleon in the
framework of covariant baryon chiral perturbation theory. We give a new upper
bound on the vacuum angle, |\theta_0| \lesssim 2.5 \cdot 10^{-10}. The quark
mass dependence of the electric dipole moment is discussed and compared to
lattice QCD data. We also perform the matching between its representations in
the three- and two-flavor theories.
