Theoretical aspects of standard model Higgs boson physics at a future $e^+ e^-$ linear collider

The Higgs boson is the missing link of the Standard Model of elementary particle physics. We review its decay properties and production mechanisms at a future e^+ e^- linear collider and its e^- e^-, e^+- gamma, and gamma gamma modes, with special emphasis on the influence of quantum corrections. We also discuss how its quantum numbers and couplings can be extracted from the study of appropriate final states