Pade approximants (PA) have been widely applied in practically all areas of physics. This work focuses on developing PA as tools for both perturbative and non-perturbative Quantum Field Theory (QFT). In perturbative QFT, a systematic estimation of higher (unknown) loop terms via asymptotic Pade approximation procedure (APAP) is established and enhanced by application to renormalization-group-(RG-)invariant quantities. This methodology is applied to hadronic Higgs decay rates (both within the Standard Model and its MSSM extension), Higgs-sector cross-sections, inclusive semileptonic decays,...