  Charginos $\tilde{\chi}^\pm$ and neutralinos $\tilde{\chi}^0$ in
supersymmetric theories can be produced copiously at $e^+e^-$ colliders and
their properties can be measured with high accuracy. Consecutively to the
chargino system, in which the SU(2) gaugino parameter $M_2$, the higgsino mass
parameter $\mu$ and $\tan\beta$ can be determined, the remaining fundamental
supersymmetry parameter in the gaugino/higgsino sector of the minimal
supersymmetric extension of the Standard Model, the U(1) gaugino mass $M_1$,
can be analyzed in the neutralino system, including its modulus and its phase
in CP-noninvariant theories. The CP properties of the neutralino system are
characterized by unitarity quadrangles. Analytical solutions for the neutralino
mass eigenvalues and for the mixing matrix are presented for CP-noninvariant
theories in general. They can be written in compact form for large
supersymmetric mass parameters. The closure of the neutralino and chargino
systems can be studied by exploiting sum rules for the pair-production
processes in $e^+e^-$ collisions. Thus the picture of the non-colored gaugino
and higgsino complex in supersymmetric theories can comprehensively be
reconstructed in these experiments.
