The role of ionization in symbiotic binaries

Processes of ionization and recombination often influence significantly the observed spectrum produced by symbiotic stars in a very wide wavelength region. Properties of the nebular spectrum provide important information on some fundamental parameters and on geometric structure of symbiotic stars. This paper reviews the recently recognized effects of ionization/recombination in these binaries and summarizes first results. We concentrate in this review on the continuum emission in the range from ultraviolet to near-IR wavelengths.