Search for Standard Model Higgs bosons produced in association with top-quark pairs in ttH¯ multilepton final states using the ATLAS detector at the LHC.

This thesis describes the search for the associated production of a Higgs boson and a top-quark pair in proton-proton collisions with a center-of-mass energy of 13 TeV. The analysis focuses on events containing two leptons with same-sing electric charge or exactly three leptons in the final state. With these requirements, the analysis is sensitive to the $H$ to $W