The normal state of Cu-O high-temperature superconductors exhibits universal anomalies that can be explained by a single hypothesis: charge- and spin-density excitations with polarizability at low frequencies proportional to ω/T. This behavior is characterized as a marginal Fermi liquid. The hypothesis leads to a self-energy that differs from conventional Fermi liquids, resulting in a quasiparticle weight that vanishes logarithmically near the Fermi surface. The spectral function is broader and has a ω⁻¹ tail, distinguishing it from a normal Fermi liquid. The normal-state properties, including resistivity, tunneling conductance, nuclear relaxation rate, specific heat, thermal conductivity, and Raman scattering, are consistent with this model. The optical conductivity is the sum of two terms, one from the Drude contribution and another from direct absorption. The results are consistent with experimental data, supporting the hypothesis that the materials are marginal Fermi liquids. The success of this phenomenology imposes constraints on microscopic theories, requiring charge and spin degrees of freedom to have similar energy scales. The behavior also suggests that perturbation theory breaks down well above the superconducting transition temperature, indicating the importance of strong interactions. The study concludes that the universal anomalies in the normal state of Cu-O superconductors are explained by the marginal Fermi liquid model.The normal state of Cu-O high-temperature superconductors exhibits universal anomalies that can be explained by a single hypothesis: charge- and spin-density excitations with polarizability at low frequencies proportional to ω/T. This behavior is characterized as a marginal Fermi liquid. The hypothesis leads to a self-energy that differs from conventional Fermi liquids, resulting in a quasiparticle weight that vanishes logarithmically near the Fermi surface. The spectral function is broader and has a ω⁻¹ tail, distinguishing it from a normal Fermi liquid. The normal-state properties, including resistivity, tunneling conductance, nuclear relaxation rate, specific heat, thermal conductivity, and Raman scattering, are consistent with this model. The optical conductivity is the sum of two terms, one from the Drude contribution and another from direct absorption. The results are consistent with experimental data, supporting the hypothesis that the materials are marginal Fermi liquids. The success of this phenomenology imposes constraints on microscopic theories, requiring charge and spin degrees of freedom to have similar energy scales. The behavior also suggests that perturbation theory breaks down well above the superconducting transition temperature, indicating the importance of strong interactions. The study concludes that the universal anomalies in the normal state of Cu-O superconductors are explained by the marginal Fermi liquid model.