The PSI Theory Group of Particle Physics mainly works on projects related to particle physics at PSI and CERN in direct connection to the activities of 3202, 3203 and 3204. Particular emphasis is put on higher-order calculations and applications of effective field theory. These methods are applied to the physics at the energy frontier (such as Higgs bosons and other Standard Model processes as well as supersymmetry and other physics beyond the Standard Model) and the low-energy high-precision frontier (QED corrections to low-energy scattering as well as lepton-flavour violating processes). This effort includes methods for the automatization of higher-order corrections. In addition, the theory group is involved in non-perturbative methods related to low-energy hadronic effects. This allows to cover aspects such as electric dipole moments of the neutron as well as hadronic effects in the anomalous magnetic moment, muonic atoms, and lepton-proton scattering.