X-ray observations of cluster outskirts: current status and future prospects

Past and current X-ray mission allow us to observe only a fraction of the volume occupied by the ICM. After reviewing the state of the art of cluster outskirts observations we discuss some important constraints that should be met when designing an experiment to measure X-ray emission out to the virial radius. From what we can surmise, WFXT is already designed to meet most of the requirements and should have no major difficulty in accommodating the remaining few.