Studies of Higgs Boson Properties in Future LHC Runs (Snowmass & ECFA studies)

After the discovery of the Higgs boson a large set of dedicated measurements is required to define its properties. In this presentation the prospects to measure Higgs boson quantum numbers, its width and self-coupling, Higgs boson couplings to gauge bosons and fermions, possible CP-mixing in the Higgs sector and also prospects to search for rare Higgs boson decays and additional BSM Higgs bosons in future LHC runs with 300 fb^{-1} and 3000 fb^{-1} of integrated luminosity are discussed.