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The X-ray absorption provides important information on the nature of the circumnuclear medium in AGNs. Understanding the physical and statistical properties of the X-ray absorption is also highly relevant to characterize the black hole accretion in the universe. Indeed, most of the AGN activity, both locally and at high redshift, is obscured. In this short paper we shortly review the main observational results in this field. Since absorption by "warm" gas is also treated by other reviews in these proceedings, "warm absorption" is only shortly discussed in Sect. 2. We will then focus on the "cold absorption", by discussing it statistical and physical properties, as well as some of the recent findings at high redshift. It is important to clarify that, due to the limited space available, this review in unavoidably highly incomplete.