For the understanding and prediction of molecular properties and chemical reactions in terms of vibration interaction, two methods, i.e., vibration mixing and vibration mapping, are proposed. Equations for vibration mixing, derived by a perturbational method, can predict qualitatively how the normal modes of fragment molecules mix with each other in the interacting system. Vibration mapping can show quantitatively how the vibration mixing in the interacting system occurs. For demonstrations, these two methods were applied to the HF-NH3 and H2CO-H2O systems.