  This paper reviews current knowledge of symbiotic binaries, with special
emphasis on their multifrequency observational characteristics, and basic
parameters of the symbiotic system components. We start with a brief
presentation of variable phenomena found in symbiotic stars. This is followed
by a summary of the recent progress in determination of their orbital and
stellar parameters. We also discuss basic properties of the symbiotic giants
compared to single evolved giants as well as the nature of the hot component
and its outburst evolution.
