To establish the Higgs mechanism {\it sui generis} experimentally, the
Higgs self-interaction potential must be reconstructed. This task
requires the measurement of the trilinear and quadrilinear
self-couplings, as predicted in the Standard Model or in
supersymmetric theories. The couplings can be probed in multiple Higgs
production at high-luminosity e+e- linear colliders. We present the
theoretical analysis for the production of neutral Higgs-boson pairs
in the relevant channels of double Higgs-strahlung and associated
multiple Higgs production.