Absorption lines are often observed in the critical central region of extragalaxies at radio wavelength bands.

They are detected against the luminous radio continuum emission associated with the central activity,

and they can provide important clues to the environment of the central region. In this talk,

I review what we have learned from radio observations towards absorption lines in the central region

of extragalaxies, and introduce our on-going observational projects on radio absorption lines.

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