In order to study strongly coupled models of electroweak symmetry breaking with a light Higgs boson, a resonance effective Lagrangian with bosonic massive resonances together with the Standard Model degrees of freedom is required. The constraints for this Lagrangian come from the phenomenology and from the assumed high-energy behavior of the underlying theory. This resonance effective theory can be used to estimate the low-energy constants (LECs) of the Electroweak Effective Theory in terms of resonance parameters and to make predictions of low-energy observables.