Galactic open clusters: key tracers of stellar structure and evolution ?

Galactic open clusters are homogeneous samples of stars with approximately the same age and chemical composition but dierent masses, eective temperatures, rotation rates and magnetic activity. They provide a fundamental tool to test models of stellar structure and evolution and to investigate the formation and chemical evolution of the galactic disk. Recent advances in the study of open clusters are reviewed with emphasis on the determination of lithium and berillium abundances as tracers of internal mixing mechanisms and on the investigation of coronal activity and evolution from the X-ray emission of cluster stars.