Abstract : This thesis work in the L3 collaboration Higgs working group contributed to the search for a Higgs signature, for center-of-mass energies between 192 and 209 GeV, one of the main goals of LEP2. It consists of a contribution to the analyses looking for the Standard Model Higgs boson, especially in the so-called "two jets plus missing energy" channel. The final state of this channel, denoted H_nu_nubar, is charaterized by the production of a pair of b quarks, from the decay of the Higgs particle, and a neutrino pair from that of the Z particle, the so-called Higgs-Strahlung process. The lower observed mass limit, obtained with the H_nu_nubar channel alone, is 96 GeV at a 95% confidence level.
In addition, searches for neutral scalar particle production are presented, in the context of general two-Higgs-doublet models of type II, by means of a "independent" analysis. Searches for "invisible" Higgs bosons are presented as well, with the Z boson decaying into a pair of fermions and the Higgs boson into undetectable particles. These results permit the constraining of the parameters of non-universal supersymmetric models (without gaugino mass unification).