In quantum field theory, penguin diagrams are a class of Feynman diagrams which are important for understanding CP violating processes in the Standard Model. They refer to one-loop processes in which a quark temporarily changes flavor, and the flavor-changed quark engages in some tree interaction, typically a strong one. For the interactions where some quark flavors have much higher interaction amplitudes than others, such as CP-violating or Higgs interactions, these penguin processes may have amplitudes comparable to or even greater than those of the direct tree processes. A similar diagram can be drawn for leptonic decays.