Centaurus A (NGC 5128) is ideal for investigating the characteristics and role of gas in an early-type galaxy in the presence of a radio-loud active nucleus. The different phases of the gas — hot (X-ray), warm (ionized), and cold (H i and molecular) — are all detected in this object and can be studied at very high spatial resolution, due to its proximity. This richness makes Centaurus A truly unique. Spatially, these gas structures span from the pc to the tens of kpc scale. Thus, they allow us to trace very different phenomena, from the formation and evolution of the host galaxy, to the interplay between nuclear activity and interstellar medium and the feeding mechanism of the central black hole. A lot of work has been done to study and understand the characteristics of the gas in this complex object, and the present paper summarizes what has been achieved so far.