Invited review given at the JENAM 2002 in Porto, Workshop ISM, eds. M.A. de Avillez & D. Breitschwerdt, Kluwer.
astro-ph/0212104.

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Abstract. Groups and clusters contain a large fraction of hot gas which emits X-ray radiation. This gas yields information on the dynamical state and on the total mass of these systems. X-ray spectra show that heavy elements are present in the gas. As these metals must have been produced in the cluster/group galaxies and later transported into the gas, the metallicity is a good tracer for the transport processes. Several possible processes, that transport gas from the small potential wells of the galaxies into the clusters and groups, are discussed.

Table of Contents

• GAS PROPERTIES
• GAS DISTRIBUTION, DYNAMICAL STATE AND MASS DETERMINATION
• INTERACTION BETWEEN ISM AND ICM/IGM
• SUMMARY
• REFERENCES