The paper by W. A. Phillips, titled "Tunneling States in Amorphous Solids," explores the linear temperature dependence of specific heat in amorphous solids at very low temperatures. The author proposes an ionic tunneling model that explains both the observed temperature dependence and the magnitude of thermal conductivity. This model also addresses the anomalous results obtained for the phonon free path through stimulated Brillouin scattering. In the introduction, Phillips highlights recent measurements of specific heat and thermal conductivity in vitreous silica, germania, and selenium, which reveal a linear temperature-dependent term in the specific heat with a consistent magnitude across these materials. He discusses the limitations of the quasimetallic contribution theory and introduces an alternative model based on tunneling states, which have been observed in alkali halides and polyethylene. The paper extends the tunneling state model to completely amorphous materials, calculating the contribution of these states to the specific heat and thermal conductivity. It also reconciles values for the phonon mean free path derived from Brillouin scattering with those from thermal conductivity. The author speculates on the microscopic origin of these tunneling states, focusing on temperatures below 1 K due to the distinct behavior observed above 1 K. In the second section, Phillips describes the tunneling states in an asymmetric potential well, detailing the distribution of energy levels and their impact on thermal properties.The paper by W. A. Phillips, titled "Tunneling States in Amorphous Solids," explores the linear temperature dependence of specific heat in amorphous solids at very low temperatures. The author proposes an ionic tunneling model that explains both the observed temperature dependence and the magnitude of thermal conductivity. This model also addresses the anomalous results obtained for the phonon free path through stimulated Brillouin scattering. In the introduction, Phillips highlights recent measurements of specific heat and thermal conductivity in vitreous silica, germania, and selenium, which reveal a linear temperature-dependent term in the specific heat with a consistent magnitude across these materials. He discusses the limitations of the quasimetallic contribution theory and introduces an alternative model based on tunneling states, which have been observed in alkali halides and polyethylene. The paper extends the tunneling state model to completely amorphous materials, calculating the contribution of these states to the specific heat and thermal conductivity. It also reconciles values for the phonon mean free path derived from Brillouin scattering with those from thermal conductivity. The author speculates on the microscopic origin of these tunneling states, focusing on temperatures below 1 K due to the distinct behavior observed above 1 K. In the second section, Phillips describes the tunneling states in an asymmetric potential well, detailing the distribution of energy levels and their impact on thermal properties.