This paper presents an effective field theory for electromagnetically or gravitationally interacting massive particles, expanding about their mass ratio. The theory integrates out the heavy particle's deviation from its inertial trajectory, resulting in an effective action with only the lighter particle and photon or graviton as degrees of freedom. The 0SF dynamics are described by the background field method, while 1SF and higher include recoil operators encoding the heavy particle's wobble. The formalism uses classical backgrounds and trajectories to extract perturbative data, validated by calculations of two-loop scattering in electromagnetism and gravity. The theory is applied to both electromagnetism and general relativity, with results for dyonic and scalar-charged particle scattering. The framework allows systematic computation of perturbative effects, including the regularization of self-force divergences. The effective action is derived for 0SF, 1SF, and 2SF orders, with the recoil operator playing a key role in describing the heavy particle's dynamics. The paper also discusses the use of this formalism in computing scattering angles and other observables, emphasizing its utility in both classical and quantum contexts.This paper presents an effective field theory for electromagnetically or gravitationally interacting massive particles, expanding about their mass ratio. The theory integrates out the heavy particle's deviation from its inertial trajectory, resulting in an effective action with only the lighter particle and photon or graviton as degrees of freedom. The 0SF dynamics are described by the background field method, while 1SF and higher include recoil operators encoding the heavy particle's wobble. The formalism uses classical backgrounds and trajectories to extract perturbative data, validated by calculations of two-loop scattering in electromagnetism and gravity. The theory is applied to both electromagnetism and general relativity, with results for dyonic and scalar-charged particle scattering. The framework allows systematic computation of perturbative effects, including the regularization of self-force divergences. The effective action is derived for 0SF, 1SF, and 2SF orders, with the recoil operator playing a key role in describing the heavy particle's dynamics. The paper also discusses the use of this formalism in computing scattering angles and other observables, emphasizing its utility in both classical and quantum contexts.