Basic physical considerations, observations and numerical simulations show that the solar chromosphere is very dynamic. The enhanced chromospheric emission, which corresponds to an outwardly increasing semiempirical temperature structure, can even be produced by wave motion without any increase in the mean gas temperature. Hence, the sun may not have a classical chromosphere in magnetic field free internetwork regions. This dynamic picture of the solar internetwork chromosphere is consistent with ground based observations of the Call resonance lines and with observations from the SOHO satellite. The simulations also show that a static picture and a dynamic picture of the chromosphere are fundamentally different and that time variations are crucial for our understanding of the chromosphere itself and the spectral features formed there. Whether the dynamic nature of the chromosphere is important for solar wind models depends on their sensitivity to chromospheric conditions. Contrary to some claims in the literature, the ionization of hydrogen in the upper chromosphere is dominated by collisional excitation in the Lyman line followed by photo-ionization by Balmer continuum photons—the Lyman continuum does not play any significant role. In the transition region, collisional ionization takes over as the major process. Ionization/recombination time-scales can be on the order of hundreds of seconds causing the ionization balance in the chromosphere to be significantly out of equilibrium with higher ionization than the equilibrium value. The hydrogen ionization zone is also considerably thicker than is claimed from dimension analyses; the ionization fraction goes from 1&percent; to 40&percent; over a height range of 600 km. ©1999 American Institute of Physics.