Relative age and absolute V mag for the GCs presently in the MW (open squares), including those associated with the Sgr dSph and for old open clusters (circles). Coloured symbols indicate clusters for which a) there is positive indication of multiple population from high-resolution spectroscopy (red) or from photometry or low-resolution spectroscopy (orange); b) there are uncertainties, but the presence is probable (magenta) or unlikely (green); and c) a negative answer has been found (light blue). A few interesting objects are labelled.