An overview of the most effective methods used for parameterization of meson-meson amplitudes below 2 GeV will be presented. Theoretical constraints imposed on the amplitudes and requirements for amplitudes will be discussed.
The most widely discussed will be the pion-pion amplitudes in all important partial waves (S, P, D and F). All these methods, constraints and new results
can greatly facilitate analysis of two body interactions in the final states, inter alia, in the photoproduction processes or decays of heavy mesons.