X-rays from Open Clusters
  The present state of X-ray observations of cool stars in coeval open clusters is reviewed. Concentrating on ROSAT results for solar-type stars, the available observational dataset is summarized along with those details of the evolution of X-ray activity of low mass stars which have been firmly established as a result. Observational questions which are as yet unresolved are then addressed, including the origin of ``supersaturation'' and whether observations of one cluster can represent the X-ray properties of all clusters at the same age. The role of high spatial resolution X-ray imaging as a tool for identifying cluster members is highlighted and the prospects for future developments with AXAF and XMM are discussed. 
R. D. Jeffries