The search for Higgs particles at LEP 2

This Habilitationsschrift is about the search for Higgs bosons, as predicted by various theoretical models, which try to explain the origin of mass. Presently this quest is one of the most important subjects of experimental as well as theoretical particle physics. In this thesis the results of the search for the standard model Higgs boson as well as for Higgs bosons of extensions of the standard model are presented. For this purpose data collected by the ALEPH experiment at the LEP2 collider have been used.