  We assess the possibility of measuring the trilinear self-coupling of the
Standard Model Higgs boson at future electron-positron linear colliders with
centre-of-mass energies between 500 and 1500 GeV. We consider rather light
Higgs scalars, with mass below the W+W- threshold, produced in the double
Higgs-strahlung channel e+e- -> HHZ and decaying via the dominant mode H ->
bbbar. Assuming ideal vertex tagging of the heavy-quark jets and mass
reconstruction of the Z boson produced in association with the Higgs pair, we
compare the yield of the above process to those of all irreducible electroweak
and strong backgrounds proceeding through a bbbar bbbar Z intermediate state.
Total cross sections and differential spectra of phenomenological relevance to
the selection and analysis of the signal are given and discussed.
