  We study dual superconductivity of the ground state of SU(2) gauge theory, in
connection with confinement. We do that measuring on the lattice a disorder
parameter describing condensation of monopoles. Confinement appears as a
transition to dual superconductor, independent of the abelian projection
defining monopoles. Some speculations are made on the existence of a more
appropriate disorder parameter. A similar study for SU(3) is presented in a
companion paper.
