Momentum space Feynman rules constitute a formal algorithmic framework for computing invariant matrix elements within Quantum Field Theory (QFT). The core principle establishes that scattering amplitudes in $\lambda\phi^4$ theory are derived by constructing diagrams comprising external legs assigned momentum flow and internal propagators defined as $i/(p^2-m^2)$, which must be integrated over unfixed loop momenta subject to conservation constraints at every vertex. This mechanism provides a systematic procedure for evaluating perturbative contributions based on functional integral components without explicit dependence on coordinate space representations.
Prerequisite chain context: requires Feynman Rules for Scalar Field Theory.